Github user bgutjahr commented on the issue:
https://github.com/apache/activemq-artemis/pull/1204
Let me first describe what I would like to have: I want to setup a number
or servers (2, maybe 3, in my case).
These servers are setup in an HA-cluster with shared store. None of them is
a dedicate master or backup server. Just the first started shall become live,
the second shall run as backup (take over after the live was stopped or died),
more additional servers waiting to become the next backup. No failback is
needed since all servers have are considered equal.
A use case would be to run the servers in an application container like
kubernetes. It will be the containers jobs to start up the servers and
automatically restart them when they stopped.
Right now, this is nearly possible: when a master server is started and
there is already a live server, it will wait (as a backup server) until it can
become life. The 'start()' method returns only after the startup is fully
complete and the server became life. The unfortunate thing about this behaviour
is that the start() methods (in EmbeddedJMS and ActiveMQServerImpl) are
synchronized. Not returning from start will kept the server object locked such
that stop() cannot be called.
This was the reason why I thought this would be a defect that I had tried
to fix. Apparently such a fix breaks backwards compatibility. So I would rather
implement an enhancement to achieve this.
(Unless you agreed that start() not returning is indeed a defect that
should be fixed).
So I can right now see a couple of alternatived to provide such a feature:
1. Add an option to the master server configuration to allow the master to
start as backup server if there is already a live server, like this:
```
<ha-policy>
<shared-store>
<master>
<allow-as-backup>true</allow-as-backup>
</master>
</shared-store>
</ha-policy>
```
1. Create a new shared-store policy type that indicates a new role (neither
master nor server), e.g.:
```
<ha-policy>
<shared-store>
<master-or-slave/>
</shared-store>
</ha-policy>
```
1. Or even don't mention such a role name at all and make it the default
behavior, like this:
```
<ha-policy>
<shared-store/>
</ha-policy>
```
What I would like to get as input:
1. Shall I make such an enhancement? If yes:
1. Which of the three alternatives should I implement - or do you rather
propose another solution?
1. For the first 2 alternatives: what should name of the option or policy
type be?
1. When adding such an enhancement, so far I know that I need to enhance
the XML schema, implement the option or policy class, implement the related
behavior, add tests, and adapt documentation. Is there anything else I'm not
aware of?
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