nodepool/doc/source/operation.rst

Operation

Nodepool has two components which run as daemons. The nodepool-builder daemon is responsible for building diskimages and uploading them to providers, and the nodepool-launcher daemon is responsible for launching and deleting nodes.

Both daemons frequently re-read their configuration file after starting to support adding or removing new images and providers, or otherwise altering the configuration.

These daemons communicate with each other via a Zookeeper database. You must run Zookeeper and at least one of each of these daemons to have a functioning Nodepool installation.

Nodepool-builder

The nodepool-builder daemon builds and uploads images to providers. It may be run on the same or a separate host as the main nodepool daemon. Multiple instances of nodepool-builder may be run on the same or separate hosts in order to speed up image builds across many machines, or supply high-availability or redundancy. However, since nodepool-builder allows specification of the number of both build and upload threads, it is usually not advantageous to run more than a single instance on one machine. Note that while diskimage-builder (which is responsible for building the underlying images) generally supports executing multiple builds on a single machine simultaneously, some of the elements it uses may not. To be safe, it is recommended to run a single instance of nodepool-builder on a machine, and configure that instance to run only a single build thread (the default).

Nodepool-launcher

The main nodepool daemon is named nodepool-launcher and is responsible for managing cloud instances launched from the images created and uploaded by nodepool-builder.

When a new image is created and uploaded, nodepool-launcher will immediately start using it when launching nodes (Nodepool always uses the most recent image for a given provider in the ready state). Nodepool will delete images if they are not the most recent or second most recent ready images. In other words, Nodepool will always make sure that in addition to the current image, it keeps the previous image around. This way if you find that a newly created image is problematic, you may simply delete it and Nodepool will revert to using the previous image.

Daemon usage

To start the main Nodepool daemon, run nodepool-launcher:

nodepool-launcher --help

To start the nodepool-builder daemon, run nodepool--builder:

nodepool-builder --help

To stop a daemon, send SIGINT to the process.

When yappi (Yet Another Python Profiler) is available, additional functions' and threads' stats are emitted as well. The first SIGUSR2 will enable yappi, on the second SIGUSR2 it dumps the information collected, resets all yappi state and stops profiling. This is to minimize the impact of yappi on a running system.

Metadata

When Nodepool creates instances, it will assign the following nova metadata:

groups

A comma separated list containing the name of the image and the name of the provider. This may be used by the Ansible OpenStack inventory plugin.

nodepool_image_name

The name of the image as a string.

nodepool_provider_name

The name of the provider as a string.

nodepool_node_id

The nodepool id of the node as an integer.

Common Management Tasks

In the course of running a Nodepool service you will find that there are some common operations that will be performed. Like the services themselves these are split into two groups, image management and instance management.

Image Management

Before Nodepool can launch any cloud instances it must have images to boot off of. nodepool dib-image-list will show you which images are available locally on disk. These images on disk are then uploaded to clouds, nodepool image-list will show you what images are bootable in your various clouds.

If you need to force a new image to be built to pick up a new feature more quickly than the normal rebuild cycle (which defaults to 24 hours) you can manually trigger a rebuild. Using nodepool image-build you can tell Nodepool to begin a new image build now. Note that depending on work that the nodepool-builder is already performing this may queue the build. Check nodepool dib-image-list to see the current state of the builds. Once the image is built it is automatically uploaded to all of the clouds configured to use that image.

At times you may need to stop using an existing image because it is broken. Your two major options here are to build a new image to replace the existing image or to delete the existing image and have Nodepool fall back on using the previous image. Rebuilding and uploading can be slow so typically the best option is to simply nodepool image-delete the most recent image which will cause Nodepool to fallback on using the previous image. Howevever, if you do this without "pausing" the image it will be immediately reuploaded. You will want to pause the image if you need to further investigate why the image is not being built correctly. If you know the image will be built correctly you can simple delete the built image and remove it from all clouds which will cause it to be rebuilt using nodepool dib-image-delete.

Command Line Tools

Usage

The general options that apply to all subcommands are:

nodepool --help

The following subcommands deal with nodepool images:

dib-image-list

nodepool dib-image-list --help

image-list

nodepool image-list --help

image-build

nodepool image-build --help

dib-image-delete

nodepool dib-image-delete --help

image-delete

nodepool image-delete --help

The following subcommands deal with nodepool nodes:

list

nodepool list --help

delete

nodepool delete --help

The following subcommands deal with ZooKeeper data management:

info

nodepool info --help

erase

nodepool erase --help

If Nodepool's database gets out of sync with reality, the following commands can help identify compute instances or images that are unknown to Nodepool:

alien-image-list

nodepool alien-image-list --help

Removing a Provider

To remove a provider, remove all of the images from that provider`s configuration (and remove all instances of that provider from any labels) and set that provider's max-servers to -1. This will instruct Nodepool to delete any images uploaded to that provider, not upload any new ones, and stop booting new nodes on the provider. You can then let the nodes go through their normal lifecycle. Once all nodes have been deleted you remove the config from nodepool for that provider entirely (though leaving it in this state is effectively the same and makes it easy to turn the provider back on).

If urgency is required you can delete the nodes directly instead of waiting for them to go through their normal lifecycle but the effect is the same.