136 lines
4.5 KiB
Markdown
136 lines
4.5 KiB
Markdown
# Overview
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The hacluster charm provides high availability for OpenStack applications that
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lack native (built-in) HA functionality. The clustering solution is based on
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Corosync and Pacemaker.
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It is a subordinate charm that works in conjunction with a principle charm that
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supports the 'hacluster' interface. The current list of such charms can be
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obtained from the [Charm Store][charms-requires-hacluster] (the charms
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officially supported by the OpenStack Charms project are published by
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'openstack-charmers').
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See [OpenStack high availability][cdg-ha] in the [OpenStack Charms Deployment
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Guide][cdg] for a comprehensive treatment of HA with charmed OpenStack.
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> **Note**: The hacluster charm is generally intended to be used with
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MAAS-based clouds.
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# Usage
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High availability can be configured in two mutually exclusive ways:
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* virtual IP(s)
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* DNS
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The virtual IP method of implementing HA requires that all units of the
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clustered OpenStack application are on the same subnet.
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The DNS method of implementing HA requires that [MAAS][upstream-maas] is used
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as the backing cloud. The clustered nodes must have static or "reserved" IP
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addresses registered in MAAS. If using a version of MAAS earlier than 2.3 the
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DNS hostname(s) should be pre-registered in MAAS before use with DNS HA.
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## Configuration
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This section covers common configuration options. See file `config.yaml` for
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the full list of options, along with their descriptions and default values.
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#### `cluster_count`
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The `cluster_count` option sets the number of hacluster units required to form
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the principle application cluster (the default is 3). It is best practice to
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provide a value explicitly as doing so ensures that the hacluster charm will
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wait until all relations are made to the principle application before building
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the Corosync/Pacemaker cluster, thereby avoiding a race condition.
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## Deployment
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At deploy time an application name should be set, and be based on the principle
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charm name (for organisational purposes):
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juju deploy hacluster <principle-charm-name>-hacluster
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A relation is then added between the hacluster application and the principle
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application.
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In the below example the VIP approach is taken. These commands will deploy a
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three-node Keystone HA cluster, with a VIP of 10.246.114.11. Each will reside
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in a container on existing machines 0, 1, and 2:
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juju deploy -n 3 --to lxd:0,lxd:1,lxd:2 --config vip=10.246.114.11 keystone
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juju deploy --config cluster_count=3 hacluster keystone-hacluster
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juju add-relation keystone-hacluster:ha keystone:ha
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## Actions
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This section lists Juju [actions][juju-docs-actions] supported by the charm.
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Actions allow specific operations to be performed on a per-unit basis.
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* `pause`
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* `resume`
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* `status`
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* `cleanup`
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* `update-ring`
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To display action descriptions run `juju actions hacluster`. If the charm is
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not deployed then see file ``actions.yaml``.
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## Presenting status information
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Here are a few examples of how to present useful information with the `status`
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action and the [jq][jq] utility.
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* Querying for `online` and `standby` parameter values:
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juju run-action --wait hacluster/leader status \
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--format json | jq '.[] | {(.UnitId):.results.result | fromjson \
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| .nodes | .[] | {unit_name: .name, online: .online, standby: .standby}}'
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output example
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{
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"hacluster/0": {
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"unit_name": "juju-a37bc0-3",
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"online": "true",
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"standby": "false"
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}
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}
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{
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"hacluster/0": {
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"unit_name": "juju-a37bc0-4",
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"online": "true",
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"standby": "false"
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}
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}
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{
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"hacluster/0": {
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"unit_name": "juju-a37bc0-5",
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"online": "true",
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"standby": "false"
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}
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}
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* Displaying cluster resource information:
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juju run-action --wait hacluster/leader status \
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--format json | jq '.[] | {(.UnitId):.results.result | fromjson \
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| .resources.groups}'
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# Bugs
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Please report bugs on [Launchpad][lp-bugs-charm-hacluster].
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For general charm questions refer to the [OpenStack Charm Guide][cg].
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<!-- LINKS -->
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[cg]: https://docs.openstack.org/charm-guide
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[lp-bugs-charm-hacluster]: https://bugs.launchpad.net/charm-hacluster/+filebug
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[juju-docs-actions]: https://juju.is/docs/olm/working-with-actions
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[cdg-ha]: https://docs.openstack.org/charm-guide/latest/admin/ha.html
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[upstream-maas]: https://maas.io
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[charms-requires-hacluster]: https://jaas.ai/search?requires=hacluster
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[cdg]: https://docs.openstack.org/project-deploy-guide/charm-deployment-guide
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[jq]: https://stedolan.github.io/jq/
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