openstack/openstack-ansible
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openstack-ansible/doc/source/install-guide/ops-galera-recovery.rst
Major Hayden c52755ef4b
Docs: Add note about slow galera recovery 
Rebuilding a galera container is stressful enough and deployers
may find that restarting the MariaDB daemon on a re-created
container takes a lot of time.

This patch adds a note to advise deployers about the time required to
sync data from the older nodes to the new, empty node. This will hopefully
restore some sanity and alleviate some stress.

Change-Id: Ife5ffed913e7ca21f7d003b7f09b740e1f678a21
2016-05-19 07:55:04 -05:00

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`Home <index.html>`_ OpenStack-Ansible Installation Guide
=======================
Galera cluster recovery
=======================
Run the `` ``galera-bootstrap`` playbook to automatically recover
a node or an entire environment. Run the ``galera install`` playbook`
using the ``galera-bootstrap`` tag to auto recover a node or an
entire environment.
#. Run the following Ansible command to show the failed nodes:
.. code-block:: shell-session
# openstack-ansible galera-install.yml --tags galera-bootstrap
The cluster comes back online after completion of this command.
Single-node failure
~~~~~~~~~~~~~~~~~~~
If a single node fails, the other nodes maintain quorum and
continue to process SQL requests.
#. Run the following Ansible command to determine the failed node:
.. code-block:: shell-session
# ansible galera_container -m shell -a "mysql -h localhost \
-e 'show status like \"%wsrep_cluster_%\";'"
node3_galera_container-3ea2cbd3 | FAILED | rc=1 >>
ERROR 2002 (HY000): Can't connect to local MySQL server through
socket '/var/run/mysqld/mysqld.sock' (111)
node2_galera_container-49a47d25 | success | rc=0 >>
Variable_name Value
wsrep_cluster_conf_id 17
wsrep_cluster_size 3
wsrep_cluster_state_uuid 338b06b0-2948-11e4-9d06-bef42f6c52f1
wsrep_cluster_status Primary
node4_galera_container-76275635 | success | rc=0 >>
Variable_name Value
wsrep_cluster_conf_id 17
wsrep_cluster_size 3
wsrep_cluster_state_uuid 338b06b0-2948-11e4-9d06-bef42f6c52f1
wsrep_cluster_status Primary
In this example, node 3 has failed.
#. Restart MariaDB on the failed node and verify that it rejoins the
cluster.
#. If MariaDB fails to start, run the ``mysqld`` command and perform
further analysis on the output. As a last resort, rebuild the container
for the node.
Multi-node failure
~~~~~~~~~~~~~~~~~~
When all but one node fails, the remaining node cannot achieve quorum and
stops processing SQL requests. In this situation, failed nodes that
recover cannot join the cluster because it no longer exists.
#. Run the following Ansible command to show the failed nodes:
.. code-block:: shell-session
# ansible galera_container -m shell -a "mysql \
-h localhost -e 'show status like \"%wsrep_cluster_%\";'"
node2_galera_container-49a47d25 | FAILED | rc=1 >>
ERROR 2002 (HY000): Can't connect to local MySQL server
through socket '/var/run/mysqld/mysqld.sock' (111)
node3_galera_container-3ea2cbd3 | FAILED | rc=1 >>
ERROR 2002 (HY000): Can't connect to local MySQL server
through socket '/var/run/mysqld/mysqld.sock' (111)
node4_galera_container-76275635 | success | rc=0 >>
Variable_name Value
wsrep_cluster_conf_id 18446744073709551615
wsrep_cluster_size 1
wsrep_cluster_state_uuid 338b06b0-2948-11e4-9d06-bef42f6c52f1
wsrep_cluster_status non-Primary
In this example, nodes 2 and 3 have failed. The remaining operational
server indicates ``non-Primary`` because it cannot achieve quorum.
#. Run the following command to
`rebootstrap <http://galeracluster.com/documentation-webpages/quorumreset.html#id1>`_
the operational node into the cluster:
.. code-block:: shell-session
# mysql -e "SET GLOBAL wsrep_provider_options='pc.bootstrap=yes';"
node4_galera_container-76275635 | success | rc=0 >>
Variable_name Value
wsrep_cluster_conf_id 15
wsrep_cluster_size 1
wsrep_cluster_state_uuid 338b06b0-2948-11e4-9d06-bef42f6c52f1
wsrep_cluster_status Primary
node3_galera_container-3ea2cbd3 | FAILED | rc=1 >>
ERROR 2002 (HY000): Can't connect to local MySQL server
through socket '/var/run/mysqld/mysqld.sock' (111)
node2_galera_container-49a47d25 | FAILED | rc=1 >>
ERROR 2002 (HY000): Can't connect to local MySQL server
through socket '/var/run/mysqld/mysqld.sock' (111)
The remaining operational node becomes the primary node and begins
processing SQL requests.
#. Restart MariaDB on the failed nodes and verify that they rejoin the
cluster:
.. code-block:: shell-session
# ansible galera_container -m shell -a "mysql \
-h localhost -e 'show status like \"%wsrep_cluster_%\";'"
node3_galera_container-3ea2cbd3 | success | rc=0 >>
Variable_name Value
wsrep_cluster_conf_id 17
wsrep_cluster_size 3
wsrep_cluster_state_uuid 338b06b0-2948-11e4-9d06-bef42f6c52f1
wsrep_cluster_status Primary
node2_galera_container-49a47d25 | success | rc=0 >>
Variable_name Value
wsrep_cluster_conf_id 17
wsrep_cluster_size 3
wsrep_cluster_state_uuid 338b06b0-2948-11e4-9d06-bef42f6c52f1
wsrep_cluster_status Primary
node4_galera_container-76275635 | success | rc=0 >>
Variable_name Value
wsrep_cluster_conf_id 17
wsrep_cluster_size 3
wsrep_cluster_state_uuid 338b06b0-2948-11e4-9d06-bef42f6c52f1
wsrep_cluster_status Primary
#. If MariaDB fails to start on any of the failed nodes, run the
``mysqld`` command and perform further analysis on the output. As a
last resort, rebuild the container for the node.
Complete failure
~~~~~~~~~~~~~~~~
Restore from backup if all of the nodes in a Galera cluster fail (do not shutdown
gracefully). Run the following command to determine if all nodes in the
cluster have failed:
.. code-block:: shell-session
# ansible galera_container -m shell -a "cat /var/lib/mysql/grastate.dat"
node3_galera_container-3ea2cbd3 | success | rc=0 >>
# GALERA saved state
version: 2.1
uuid: 338b06b0-2948-11e4-9d06-bef42f6c52f1
seqno: -1
cert_index:
node2_galera_container-49a47d25 | success | rc=0 >>
# GALERA saved state
version: 2.1
uuid: 338b06b0-2948-11e4-9d06-bef42f6c52f1
seqno: -1
cert_index:
node4_galera_container-76275635 | success | rc=0 >>
# GALERA saved state
version: 2.1
uuid: 338b06b0-2948-11e4-9d06-bef42f6c52f1
seqno: -1
cert_index:
All the nodes have failed if ``mysqld`` is not running on any of the
nodes and all of the nodes contain a ``seqno`` value of -1.
If any single node has a positive ``seqno`` value, then that node can be
used to restart the cluster. However, because there is no guarantee that
each node has an identical copy of the data, we do not recommend to
restart the cluster using the ``--wsrep-new-cluster`` command on one
node.
Rebuilding a container
~~~~~~~~~~~~~~~~~~~~~~
Recovering from certain failures require rebuilding one or more containers.
#. Disable the failed node on the load balancer.
.. note::
Do not rely on the load balancer health checks to disable the node.
If the node is not disabled, the load balancer sends SQL requests
to it before it rejoins the cluster and cause data inconsistencies.
#. Destroy the container and remove MariaDB data stored outside
of the container:
.. code-block:: shell-session
# lxc-stop -n node3_galera_container-3ea2cbd3
# lxc-destroy -n node3_galera_container-3ea2cbd3
# rm -rf /openstack/node3_galera_container-3ea2cbd3/*
In this example, node 3 failed.
#. Run the host setup playbook to rebuild the container on node 3:
.. code-block:: shell-session
# openstack-ansible setup-hosts.yml -l node3 \
-l node3_galera_container-3ea2cbd3
The playbook restarts all other containers on the node.
#. Run the infrastructure playbook to configure the container
specifically on node 3:
.. code-block:: shell-session
# openstack-ansible setup-infrastructure.yml \
-l node3_galera_container-3ea2cbd3
.. warning::
The new container runs a single-node Galera cluster, which is a dangerous
state because the environment contains more than one active database
with potentially different data.
.. code-block:: shell-session
# ansible galera_container -m shell -a "mysql \
-h localhost -e 'show status like \"%wsrep_cluster_%\";'"
node3_galera_container-3ea2cbd3 | success | rc=0 >>
Variable_name Value
wsrep_cluster_conf_id 1
wsrep_cluster_size 1
wsrep_cluster_state_uuid da078d01-29e5-11e4-a051-03d896dbdb2d
wsrep_cluster_status Primary
node2_galera_container-49a47d25 | success | rc=0 >>
Variable_name Value
wsrep_cluster_conf_id 4
wsrep_cluster_size 2
wsrep_cluster_state_uuid 338b06b0-2948-11e4-9d06-bef42f6c52f1
wsrep_cluster_status Primary
node4_galera_container-76275635 | success | rc=0 >>
Variable_name Value
wsrep_cluster_conf_id 4
wsrep_cluster_size 2
wsrep_cluster_state_uuid 338b06b0-2948-11e4-9d06-bef42f6c52f1
wsrep_cluster_status Primary
#. Restart MariaDB in the new container and verify that it rejoins the
cluster.
.. note::
In larger deployments, it may take some time for the MariaDB daemon to
start in the new container. It will be synchronizing data from the other
MariaDB servers during this time. You can monitor the status during this
process by tailing the ``/var/log/mysql_logs/galera_server_error.log``
log file.
Lines starting with ``WSREP_SST`` will appear during the sync process
and you should see a line with ``WSREP: SST complete, seqno: <NUMBER>``
if the sync was successful.
.. code-block:: shell-session
# ansible galera_container -m shell -a "mysql \
-h localhost -e 'show status like \"%wsrep_cluster_%\";'"
node2_galera_container-49a47d25 | success | rc=0 >>
Variable_name Value
wsrep_cluster_conf_id 5
wsrep_cluster_size 3
wsrep_cluster_state_uuid 338b06b0-2948-11e4-9d06-bef42f6c52f1
wsrep_cluster_status Primary
node3_galera_container-3ea2cbd3 | success | rc=0 >>
Variable_name Value
wsrep_cluster_conf_id 5
wsrep_cluster_size 3
wsrep_cluster_state_uuid 338b06b0-2948-11e4-9d06-bef42f6c52f1
wsrep_cluster_status Primary
node4_galera_container-76275635 | success | rc=0 >>
Variable_name Value
wsrep_cluster_conf_id 5
wsrep_cluster_size 3
wsrep_cluster_state_uuid 338b06b0-2948-11e4-9d06-bef42f6c52f1
wsrep_cluster_status Primary
#. Enable the failed node on the load balancer.
--------------
.. include:: navigation.txt
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