Apply HA section template to README
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README.md
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README.md
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@ -54,42 +54,17 @@ server through the `mysql-shared` interface. When a new data store is
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configured, the charm ensures the minimum administrator credentials exist (as
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configured in charm configuration)
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## HA/Clustering
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## High availability
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There are two mutually exclusive high availability options: using virtual
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IP(s) or DNS. In both cases, a relationship to hacluster is required which
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provides the corosync backend HA functionality.
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When more than one unit is deployed with the [hacluster][hacluster-charm]
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application the charm will bring up an HA active/active cluster.
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To use virtual IP(s), the clustered nodes must be on the same subnet such that
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the VIP is a valid IP on the subnet for one of the node's interfaces and each
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node has an interface in said subnet. The VIP becomes a highly-available API
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endpoint.
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There are two mutually exclusive high availability options: using virtual IP(s)
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or DNS. In both cases the hacluster subordinate charm is used to provide the
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Corosync and Pacemaker backend HA functionality.
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At a minimum, the config option `vip` must be set in order to use virtual IP
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HA. If multiple networks are being used, a VIP should be provided for each
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network, separated by spaces. Optionally, `vip_iface` or `vip_cidr` may be
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specified.
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To use DNS high availability, there are several prerequisites. However, DNS HA
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does not require the clustered nodes to be on the same subnet.
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Currently, the DNS HA feature is only available for MAAS 2.0 or greater
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environments. MAAS 2.0 requires Juju 2.0 or greater. The clustered nodes must
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have static or "reserved" IP addresses registered in MAAS. The DNS hostname(s)
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must be pre-registered in MAAS before use with DNS HA.
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At a minimum, the configuration option `dns-ha` must be set to true and at
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least one of `os-public-hostname`, `os-internal-hostname` or
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`os-admin-hostname` must be set in order to use DNS HA. One or more of the
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above hostnames may be set.
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The charm will throw an exception in the following circumstances:
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- If neither `vip` nor `dns-ha` is set and the charm is related to hacluster
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- If both `vip` and `dns-ha` are set as they are mutually exclusive
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- If `dns-ha` is set and none of the `os-{admin,internal,public}-hostname`
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configuration options are set
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See [OpenStack high availability][cdg-ha-apps] in the [OpenStack Charms
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Deployment Guide][cdg] for details.
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## TLS/HTTPS
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@ -331,8 +306,10 @@ For general charm questions refer to the OpenStack [Charm Guide][cg].
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<!-- LINKS -->
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[hacluster-charm]: https://jaas.ai/hacluster
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[cg]: https://docs.openstack.org/charm-guide
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[cdg]: https://docs.openstack.org/project-deploy-guide/charm-deployment-guide
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[cdg-appendix-n]: https://docs.openstack.org/project-deploy-guide/charm-deployment-guide/latest/app-policy-overrides.html
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[lp-bugs-charm-keystone]: https://bugs.launchpad.net/charm-keystone/+filebug
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[SCPD]: https://docs.openstack.org/keystone/latest/admin/configuration.html#security-compliance-and-pci-dss
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[cdg-ha-apps]: https://docs.openstack.org/project-deploy-guide/charm-deployment-guide/latest/app-ha.html#ha-applications
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