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:title: OpenAFS
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.. _openafs:
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OpenAFS
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#######
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The Andrew Filesystem (or AFS) is a global distributed filesystem.
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With a single mountpoint, clients can access any site on the Internet
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which is running AFS as if it were a local filesystem.
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OpenAFS is an open source implementation of the AFS services and
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utilities.
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A collection of AFS servers and volumes that are collectively
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administered within a site is called a ``cell``. The OpenStack
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project runs the ``openstack.org`` AFS cell, accessible at
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``/afs/openstack.org/``.
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At a Glance
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===========
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:Hosts:
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* afsdb01.openstack.org (a vldb and pts server in DFW)
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* afsdb02.openstack.org (a vldb and pts server in ORD)
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* afs01.dfw.openstack.org (a fileserver in DFW)
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* afs02.dfw.openstack.org (a second fileserver in DFW)
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* afs01.ord.openstack.org (a fileserver in ORD)
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:Puppet:
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* https://opendev.org/opendev/puppet-openafs
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* :git_file:`modules/openstack_project/manifests/afsdb.pp`
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* :git_file:`modules/openstack_project/manifests/afsfs.pp`
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:Projects:
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* http://openafs.org/
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:Bugs:
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* http://bugs.launchpad.net/openstack-ci
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* http://rt.central.org/rt/Search/Results.html?Order=ASC&DefaultQueue=10&Query=Queue%20%3D%20%27openafs-bugs%27%20AND%20%28Status%20%3D%20%27open%27%20OR%20Status%20%3D%20%27new%27%29&Rows=50&OrderBy=id&Page=1&Format=&user=guest&pass=guest
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:Resources:
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* `OpenAFS Documentation <http://docs.openafs.org/index.html>`_
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OpenStack Cell
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--------------
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AFS may be one of the most thoroughly documented systems in the world.
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There is plenty of very good information about how AFS works and the
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commands to use it. This document will only cover the minimum needed
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to understand our deployment of it.
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OpenStack runs an AFS cell called ``openstack.org``. There are three
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important services provided by a cell: the volume location database
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(VLDB), the protection database (PTS), and the file server (FS). The
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volume location service answers queries from clients about which
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fileservers should be contacted to access particular volumes, while
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the protection service provides information about users and groups.
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Our implementation follows the common recommendation to colocate the
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VLDB and PTS servers, and so they both run on our afsdb* servers.
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These servers all have the same information and communicate with each
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other to keep in sync and automatically provide high-availability
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service. For that reason, one of our DB servers is in the DFW region,
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and the other in ORD.
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Fileservers contain volumes, each of which is a portion of the file
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space provided by that cell. A volume appears as at least one
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directory, but may contain directories within the volume. Volumes are
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mounted within other volumes to construct the filesystem hierarchy of
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the cell.
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OpenStack has two fileservers in DFW and one in ORD. They do not
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automatically contain copies of the same data. A read-write volume in
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AFS can only exist on exactly one fileserver, and if that fileserver
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is out of service, the volumes it serves are not available. However,
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volumes may have read-write copies which are stored on other
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fileservers. If a client requests a read-only volume, as long as one
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site with a read-only volume is online, it will be available.
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Client Configuration
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--------------------
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.. _afs_client:
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To use OpenAFS on a Debian or Ubuntu machine::
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sudo apt-get install openafs-client openafs-krb5 krb5-user
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Debconf will ask you for a default realm, cell and cache size.
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Answer::
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Default Kerberos version 5 realm: OPENSTACK.ORG
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AFS cell this workstation belongs to: openstack.org
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Size of AFS cache in kB: 500000
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The default cache size in debconf is 50000 (50MB) which is not very
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large. We recommend setting it to 500000 (500MB -- add a zero to the
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default debconf value), or whatever is appropriate for your system.
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The OpenAFS client is not started by default, so you will need to
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run::
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sudo service openafs-client start
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When it's done, you should be able to ``cd /afs/openstack.org``.
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Most of what is in our AFS cell does not require authentication.
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However, if you have a principal in kerberos, you can get an
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authentication token for use with AFS with::
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kinit
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aklog
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If not running on Debian or Ubuntu you can install openafs client
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packages as well as Kerberos5 packages on your distro of choice.
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Then to kinit, use your fully qualified user id::
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kinit $USERNAME@OPENSTACK.ORG
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Or for admin access::
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kinit $USERNAME/admin@OPENSTACK.ORG
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Then aklog, specifying the openstack.org cell::
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aklog -cell openstack.org
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Administration
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--------------
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The following information is relevant to AFS administrators.
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All of these commands have excellent manpages which can be accessed
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with commands like ``man vos`` or ``man vos create``. They also
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provide short help messages when run like ``vos -help`` or ``vos
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create -help``.
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For all administrative commands, you may either run them from any AFS
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client machine while authenticated as an AFS admin, or locally without
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authentication on an AFS server machine by appending the `-localauth`
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flag to the end of the command.
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Adding a User
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~~~~~~~~~~~~~
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First, add a kerberos principal as described in :ref:`addprinc`. Have the
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username and UID from puppet ready.
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Then add the user to the protection database with::
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pts createuser $USERNAME -id UID
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Admin UIDs start at 1 and increment. If you are adding a new admin
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user, you must run ``pts listentries``, find the highest UID for an
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admin user, increment it by one and use that as the UID. The username
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for an admin user should be in the form ``username.admin``.
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.. note::
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Any '/' characters in a kerberos principal become '.' characters in
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AFS.
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Adding a Superuser
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~~~~~~~~~~~~~~~~~~
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Run the following commands to add an existing principal to AFS as a
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superuser::
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bos adduser -server afsdb01.openstack.org -user $USERNAME.admin
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bos adduser -server afsdb02.openstack.org -user $USERNAME.admin
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bos adduser -server afs01.dfw.openstack.org -user $USERNAME.admin
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bos adduser -server afs02.dfw.openstack.org -user $USERNAME.admin
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bos adduser -server afs01.ord.openstack.org -user $USERNAME.admin
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pts adduser -user $USERNAME.admin -group system:administrators
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Deleting Files
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~~~~~~~~~~~~~~
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.. note::
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This is a basic example of write operations for AFS-hosted
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content, so applies more generally to manually adding or changing
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files as well. As we semi-regularly get requests to delete
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subtrees of documentation, this serves as a good demonstration.
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First, as a prerequisite, make sure you've followed the `Client
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Configuration`_ and `Adding a Superuser`_ steps for yourself and
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that you know the password for your ``$USERNAME/admin`` kerberos
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principal. Safely authenticate your superuser's principal in a new
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PAG as follows::
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pagsh -c /bin/bash
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export KRB5CCNAME=FILE:`mktemp`
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kinit $USERNAME/admin
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aklog
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If this is a potentially destructive change (perhaps you're worried
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you might mistype a deletion and remove more content than you
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intended) you can first create a copy-on-write backup snapshot like
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so::
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vos backup docs
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When deleting files, note that you should use the read-write
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``/afs/.openstack.org`` path rather than the read-only
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``/afs/openstack.org`` path, but normal Unix file manipulation
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commands work as expected (do _not_ use ``sudo`` for this)::
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rm -rf /afs/.openstack.org/docs/project-install-guide/baremetal/draft
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If you don't want to have to wait for a volume release to happen (so
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that your changes to the read-write filesystem are reflected
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immediately in the read-only filesystem), you can release it now
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too::
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vos release docs -verbose
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Now you can clean up your session, destroy your ticket and exit the
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temporary PAG thusly::
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unlog
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kdestroy
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exit
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Creating a Volume
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~~~~~~~~~~~~~~~~~
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Select a fileserver for the read-write copy of the volume according to
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which region you wish to locate it after ensuring it has sufficient
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free space. Then run::
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vos create $FILESERVER a $VOLUMENAME
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The `a` in the preceding command tells it to place the volume on
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partition `vicepa`. Our fileservers only have one partition and therefore
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this is a constant.
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Be sure to mount the read-write volume in AFS with::
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fs mkmount /afs/.openstack.org/path/to/mountpoint $VOLUMENAME
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You may want to create read-only sites for the volume with ``vos
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addsite`` and then ``vos release``.
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If the volume's mountpoint lies within another volume, you may also
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need to ``vos release`` that parent volume before it will show up in
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the read-only path.
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You should set the volume quota with ``fs setquota``.
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Adding a Fileserver
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~~~~~~~~~~~~~~~~~~~
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Put the machine's public IP on a single line in
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/var/lib/openafs/local/NetInfo (TODO: puppet this).
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Copy ``/etc/openafs/server/*`` from an existing fileserver.
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Create an LVM volume named ``vicepa`` from cinder volumes. See
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:ref:`cinder` for details on volume management. Then run::
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mkdir /vicepa
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echo "/dev/main/vicepa /vicepa ext4 errors=remount-ro,barrier=0 0 2" >>/etc/fstab
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mount -a
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Finally, create the fileserver with::
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bos create -server NEWSERVER -instance dafs -type dafs \
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-cmd "/usr/lib/openafs/dafileserver -L -p 242 -busyat 600 -rxpck 700 \
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-s 1200 -l 1200 -cb 1500000 -b 240 -vc 1200 \
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-udpsize 131071 -sendsize 131071" \
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-cmd /usr/lib/openafs/davolserver \
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-cmd /usr/lib/openafs/salvageserver \
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-cmd /usr/lib/openafs/dasalvager
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It is worth evaluating these settings periodically
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* ``-L`` selects the large size, which ups a number of defaults
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* ``-p`` defines the worker threads for processing incoming calls.
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Since they block until there is work to do, we should leave this at
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around the maximum (which may increase across versions; see
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documentation)
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* ``-udpsize`` and ``-sendsize`` should be increased above their default
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* ``-cb`` defines the callbacks. For our use case, with a single
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mirror writer, this should be around the number of files the client
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is configured to cache (``-dcache``) multiplied by the number of
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clients.
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Updating Settings
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~~~~~~~~~~~~~~~~~
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If you wish to update the settings for an existing server, you can
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stop and remove the existing ``bnode`` (the collection of processes
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the overseer is monitoring, created via ``bos create`` above) and
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recreate it.
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For example ::
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bos stop -server afs01.dfw.openstack.org \
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-instance dafs \
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-wait
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Then remove the server with ::
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bos delete -server afs01.dfw.openstack.org \
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-instance dafs
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Finally run the ``bos create`` command above with any modified
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parameters to restart the server.
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Mirrors
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~~~~~~~
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We host mirrors in AFS so that we store only one copy of the data, but
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mirror servers local to each cloud region in which we operate serve
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that data to nearby hosts from their local cache.
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All of our mirrors are housed under ``/afs/openstack.org/mirror``.
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Each mirror is on its own volume, and each with a read-only replica.
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This allows mirrors to be updated and then the read-only replicas
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atomically updated. Because mirrors are typically very large and
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replication across regions is slow, we place both copies of mirror
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data on two fileservers in the same region. This allows us to perform
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maintenance on fileservers hosting mirror data as well deal with
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outages related to a single server, but does not protect the mirror
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system from a region-wide outage.
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In order to establish a new mirror, do the following:
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* The following commands need to be run authenticated on a host with
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kerberos and AFS setup (see `afs_client`_; admins can run the
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commands on ``mirror-update.openstack.org``). Firstly ``kinit`` and
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``aklog`` to get tokens.
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* Create the mirror volume. See `Creating a Volume`_ for details.
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The volume should be named ``mirror.foo``, where `foo` is
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descriptive of the contents of the mirror. Example::
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vos create afs01.dfw.openstack.org a mirror.foo
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* Create read-only replicas of the volume. One replica should be
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located on the same fileserver (it will take little to no additional
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space), and at least one other replica on a different fileserver.
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Example::
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vos addsite afs01.dfw.openstack.org a mirror.foo
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vos addsite afs02.dfw.openstack.org a mirror.foo
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* Release the read-only replicas::
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vos release mirror.foo
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See the status of all volumes with::
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vos listvldb
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When traversing from a read-only volume to another volume across a
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mountpoint, AFS will first attempt to use a read-only replica of the
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destination volume if one exists. In order to naturally cause clients
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to prefer our read-only paths for mirrors, the entire path up to that
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point is composed of read-only volumes::
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/afs [root.afs]
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/openstack.org [root.cell]
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/mirror [mirror]
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/bar [mirror.bar]
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In order to mount the ``mirror.foo`` volume under ``mirror`` we need
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to modify the read-write version of the ``mirror`` volume. To make
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this easy, the read-write version of the cell root is mounted at
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``/afs/.openstack.org``. Following the same logic from earlier,
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traversing to paths below that mount point will generally prefer
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read-write volumes.
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* Mount the volume into afs using the read-write path::
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fs mkmount /afs/.openstack.org/mirror/foo mirror.foo
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* Release the ``mirror`` volume so that the (currently empty) foo
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mirror itself appears in directory listings under
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``/afs/openstack.org/mirror``::
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vos release mirror
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* Create a principal for the mirror update process. See
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:ref:`addprinc` for details. The principal should be called
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``service/foo-mirror``. Example::
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kadmin: addprinc -randkey service/foo-mirror@OPENSTACK.ORG
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kadmin: ktadd -k /path/to/foo.keytab service/foo-mirror@OPENSTACK.ORG
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* Add the service principal's keytab to hiera. Copy the binary key to
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``bridge.openstack.org`` and then use ``hieraedit`` to update
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the files
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.. code-block:: console
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root@bridge:~# /opt/system-config/tools/hieraedit.py \
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--yaml /etc/ansible/hosts/host_vars/mirror-update.openstack.org.yaml \
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-f /path/to/foo.keytab KEYNAME
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(don't forget to ``git commit`` and save the change; you can remove
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the copies of the binary key too). The key will be base64 encoded
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in the heira database. If you need to examine it for some reason
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you can use ``base64``::
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cat /path/to/foo.keytab | base64
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* Add the new key to ``mirror-update.openstack.org`` in
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``manifests/site.pp`` for the mirror scripts to use during update.
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* Create an AFS user for the service principal::
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pts createuser service.foo-mirror
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Because mirrors usually have a large number of directories, it is best
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to avoid frequent ACL changes. To this end, we grant access to the
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mirror directories to a group where we can easily modify group
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membership if our needs change.
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* Create a group to contain the service principal, and add the
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principal::
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pts creategroup foo-mirror
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pts adduser service.foo-mirror foo-mirror
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View users, groups, and their membership with::
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pts listentries
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pts listentries -group
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pts membership foo-mirror
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* Grant the group access to the mirror volume::
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fs setacl /afs/.openstack.org/mirror/foo foo-mirror write
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* Grant anonymous users read access::
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fs setacl /afs/.openstack.org/mirror/foo system:anyuser read
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* Set the quota on the volume (e.g., 100GB)::
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fs setquota /afs/.openstack.org/mirror/foo 100000000
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Because the initial replication may take more time than we allocate in
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our mirror update cron jobs, manually perform the first mirror update:
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* In screen, obtain the lock on ``mirror-update.openstack.org``::
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flock -n /var/run/foo-mirror/mirror.lock bash
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Leave that running while you perform the rest of the steps.
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* Also in screen on ``mirror-update``, run the initial mirror sync.
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If using one of the mirror update scripts (from ``/usr/local/bin``)
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be aware that they generally run the update process under
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``timeout`` with shorter periods than may be required for the
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initial full sync. e.g. for ``reprepro`` mirrors
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NO_TIMEOUT=1 /usr/local/bin/reprepro-mirror-update /etc/reprepro/ubuntu mirror.ubuntu
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* Log into ``afs01.dfw.openstack.org`` and run ``screen``. Within
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that session, periodically during the sync, and once again after it
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is complete, run::
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vos release mirror.foo -localauth
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It is important to do this from an AFS server using ``-localauth``
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rather than your own credentials and inside of screen because if
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``vos release`` is interrupted, it will require some manual cleanup
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(data will not be corrupted, but clients will not see the new volume
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until it is successfully released). Additionally, ``vos release`` has
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a bug where it will not use renewed tokens and so token expiration
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during a vos release may cause a similar problem.
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* Once the initial sync and ``vos release`` are complete, release
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the lock file on mirror-update.
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Removing a mirror
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~~~~~~~~~~~~~~~~~
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If you need to remove a mirror, you can do the following:
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* Unmount the volume from the R/W location::
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fs rmmount /afs/.openstack.org/mirror/foo
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* Release the R/O mirror volume to reflect the changes::
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vos release mirror
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* Check what servers the volumes are on with ``vos listvldb``::
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VLDB entries for all servers
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...
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mirror.foo
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RWrite: 536870934 ROnly: 536870935
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number of sites -> 3
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server afs01.dfw.openstack.org partition /vicepa RW Site
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server afs01.dfw.openstack.org partition /vicepa RO Site
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server afs01.ord.openstack.org partition /vicepa RO Site
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...
|
|
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* Remove the R/O replicas (you can also see these with ``vos
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listvol -server afs0[1|2].dfw.openstack.org``)::
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|
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vos remove -server afs01.dfw.openstack.org -partition a -id mirror.foo.readonly
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vos remove -server afs02.dfw.openstack.org -partition a -id mirror.foo.readonly
|
|
|
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* Remove the R/W volume::
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|
|
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vos remove -server afs02.dfw.openstack.org -partition a -id mirror.foo
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|
|
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Reverse Proxy Cache
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|
^^^^^^^^^^^^^^^^^^^
|
|
|
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* `modules/openstack_project/templates/mirror.vhost.erb
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<https://opendev.org/opendev/system-config/src/branch/master/modules/openstack_project/templates/mirror.vhost.erb>`__
|
|
|
|
Each of the region-local mirror hosts exposes a limited reverse HTTP
|
|
proxy on port 8080. These proxies run within the same Apache setup as
|
|
used to expose AFS mirror contents. `mod_cache
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|
<https://httpd.apache.org/docs/2.4/mod/mod_proxy.html>`__ is used to
|
|
expose a white-listed set of resources (currently just RDO).
|
|
|
|
Currently they will cache data for up to 24 hours (Apache default)
|
|
with pruning performed by ``htcacheclean`` once an hour to keep the
|
|
cache size at or under 2GB of disk space.
|
|
|
|
The reverse proxy is provided because there are some hosted resources
|
|
that are not currently able to be practically mirrored. Examples of
|
|
this include RDO (rsync from RDO is slow and they update frequently)
|
|
and docker images (which require specialized software to run a docker
|
|
registry and then sorting out how to run that on a shared filesystem).
|
|
|
|
Apache was chosen because we already had configuration management in
|
|
place for Apache on these hosts. This avoids management overheads of
|
|
a completely new service deployment such as Squid or a caching docker
|
|
registry daemon.
|
|
|
|
No Outage Server Maintenance
|
|
----------------------------
|
|
|
|
afsdb0X.openstack.org
|
|
~~~~~~~~~~~~~~~~~~~~~
|
|
|
|
We have redundant AFS DB servers. You can take one down without causing
|
|
a service outage as long as the other remains up. To do this safely::
|
|
|
|
root@afsdb01:~# bos shutdown afsdb01.openstack.org -wait -localauth
|
|
root@afsdb01:~# bos status afsdb01.openstack.org -localauth
|
|
Instance ptserver, temporarily disabled, currently shutdown.
|
|
Instance vlserver, temporarily disabled, currently shutdown.
|
|
|
|
Then perform your maintenance on afsdb01. When done a reboot will
|
|
automatically restart the bos service or you can manually restart
|
|
the openafs-fileserver service::
|
|
|
|
root@afsdb01:~# service openafs-fileserver start
|
|
|
|
Finally check that the service is back up and running::
|
|
|
|
root@afsdb01:~# bos status afsdb01.openstack.org -localauth
|
|
Instance ptserver, currently running normally.
|
|
Instance vlserver, currently running normally.
|
|
|
|
Now you can repeat the process against afsdb02.
|
|
|
|
afs0X.openstack.org
|
|
~~~~~~~~~~~~~~~~~~~
|
|
|
|
Taking down the actual fileservers is slightly more complicated
|
|
but works similarly. Basically what we need to do is make sure that
|
|
either no one needs the RW volumes hosted by a fileserver before
|
|
taking it down or move the RW volume to another fileserver.
|
|
|
|
To ensure nothing needs the RW volumes you can hold the various
|
|
file locks on hosts that publish to AFS and/or remove cron entries
|
|
that perform vos releases or volume writes.
|
|
|
|
If instead you need to move the RW volume first step is checking
|
|
where the volumes live::
|
|
|
|
root@afsdb01:~# vos listvldb -localauth
|
|
VLDB entries for all servers
|
|
|
|
mirror
|
|
RWrite: 536870934 ROnly: 536870935
|
|
number of sites -> 3
|
|
server afs01.dfw.openstack.org partition /vicepa RW Site
|
|
server afs01.dfw.openstack.org partition /vicepa RO Site
|
|
server afs01.ord.openstack.org partition /vicepa RO Site
|
|
|
|
We see that if we want to allow write to the mirror volume and take
|
|
down afs01.dfw.openstack.org we will have to move the volume to one
|
|
of the other servers::
|
|
|
|
root@afsdb01:~# screen # use screen as this may take quite some time.
|
|
root@afsdb01:~# vos move -id mirror -toserver afs01.ord.openstack.org -topartition vicepa -fromserver afs01.dfw.openstack.org -frompartition vicepa -localauth
|
|
|
|
When that is done (use listvldb command above to check) it is now safe
|
|
to take down afs01.dfw.openstack.org while having writers to the mirror
|
|
volume. We use the same process as for the db server::
|
|
|
|
root@afsdb01:~# bos shutdown afs01.dfw.openstack.org -localauth
|
|
root@afsdb01:~# bos status afsdb01.dfw.openstack.org -localauth
|
|
Auxiliary status is: file server shut down.
|
|
|
|
Perform maintenance, then restart as above and check the status again::
|
|
|
|
root@afsdb01:~# bos status afsdb01.dfw.openstack.org -localauth
|
|
Auxiliary status is: file server running.
|
|
|
|
DNS Entries
|
|
-----------
|
|
|
|
AFS uses the following DNS entries::
|
|
|
|
_afs3-prserver._udp.openstack.org. 300 IN SRV 10 10 7002 afsdb01.openstack.org.
|
|
_afs3-prserver._udp.openstack.org. 300 IN SRV 10 10 7002 afsdb02.openstack.org.
|
|
_afs3-vlserver._udp.openstack.org. 300 IN SRV 10 10 7003 afsdb01.openstack.org.
|
|
_afs3-vlserver._udp.openstack.org. 300 IN SRV 10 10 7003 afsdb02.openstack.org.
|
|
|
|
Be sure to update them if volume location and PTS servers change. Also note
|
|
that only A (IPv4 address) records are used in the SRV data. Since OpenAFS
|
|
lacks support for IPv6, avoid entering corresponding AAAA (IPv6 address)
|
|
records for these so that it won't cause fallback delays for other
|
|
v6-supporting AFS client implementations.
|