openstack/charm-heat
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Apply HA section template to README

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Peter Matulis 2020-05-29 13:55:56 -04:00
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README.md
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@ -26,38 +26,17 @@ If using juju 1.x run:
This is only required for >= OpenStack Kilo.
## HA/Clustering
## High availability
There are two mutually exclusive high availability options: using virtual
IP(s) or DNS. In both cases, a relationship to hacluster is required which
provides the corosync back end HA functionality.
When more than one unit is deployed with the [hacluster][hacluster-charm]
application the charm will bring up an HA active/active cluster.
To use virtual IP(s) the clustered nodes must be on the same subnet such that
the VIP is a valid IP on the subnet for one of the node's interfaces and each
node has an interface in said subnet. The VIP becomes a highly-available API
endpoint.
There are two mutually exclusive high availability options: using virtual IP(s)
or DNS. In both cases the hacluster subordinate charm is used to provide the
Corosync and Pacemaker backend HA functionality.
At a minimum, the config option 'vip' must be set in order to use virtual IP
HA. If multiple networks are being used, a VIP should be provided for each
network, separated by spaces. Optionally, vip_iface or vip_cidr may be
specified.
To use DNS high availability there are several prerequisites. However, DNS HA
does not require the clustered nodes to be on the same subnet.
Currently the DNS HA feature is only available for MAAS 2.0 or greater
environments. MAAS 2.0 requires Juju 2.0 or greater. The clustered nodes must
have static or "reserved" IP addresses registered in MAAS. The DNS hostname(s)
must be pre-registered in MAAS before use with DNS HA.
At a minimum, the config option 'dns-ha' must be set to true and at least one
of 'os-public-hostname', 'os-internal-hostname' or 'os-internal-hostname' must
be set in order to use DNS HA. One or more of the above hostnames may be set.
The charm will throw an exception in the following circumstances:
If neither 'vip' nor 'dns-ha' is set and the charm is related to hacluster
If both 'vip' and 'dns-ha' are set as they are mutually exclusive
If 'dns-ha' is set and none of the os-{admin,internal,public}-hostname(s) are
set
See [OpenStack high availability][cdg-ha-apps] in the [OpenStack Charms
Deployment Guide][cdg] for details.
## Spaces
@ -135,3 +114,5 @@ For general charm questions refer to the OpenStack [Charm Guide][cg].
[cdg]: https://docs.openstack.org/project-deploy-guide/charm-deployment-guide
[cdg-appendix-n]: https://docs.openstack.org/project-deploy-guide/charm-deployment-guide/latest/app-policy-overrides.html
[lp-bugs-charm-heat]: https://bugs.launchpad.net/charm-heat/+filebug
[hacluster-charm]: https://jaas.ai/hacluster
[cdg-ha-apps]: https://docs.openstack.org/project-deploy-guide/charm-deployment-guide/latest/app-ha.html#ha-applications