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https://issues.apache.org/jira/browse/WHIRR-693?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13569704#comment-13569704
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Steve Loughran commented on WHIRR-693:
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# This could be good for more complex deployments, though there's a risk of
workflow-related feature creep (see below).
# This could mark the time for moving beyond .properties files, as with
multiple templates, overridden attributes and now sequences, the requirements
of more configuration management languages crop up. Rather than propose a new
one, have a look at JSON.
# There really needs to be probes in Whirr to trigger starting one phase on the
observed state of the previous set. That way rather than just saying "run
HDFS", the HDFS phase is considered to have successfully completed when a probe
of the NN returned the filesystem was up (Hitting URLS and getting 200
responses is the single most relevant probe here).
# Teardown gets trickier as you'd have to go back in order from what state you
got to, worry about timing etc. This is why a "say no to teardown" policy,
relying on the PaaS infrastructure to kill your VMs, is the only rational
tactic here.
Having probes to defined the barriers between phases -I'm using that term as
its the traditional one- makes it possible to define phase transition not as
"all the previously started action scripts finished", but "the cluster was put
in the state we needed for the next actions". URLs are the obvious choice
> Control order of actions with waves of whirr.instance-templates
> ---------------------------------------------------------------
>
> Key: WHIRR-693
> URL: https://issues.apache.org/jira/browse/WHIRR-693
> Project: Whirr
> Issue Type: Bug
> Components: core
> Reporter: Paul Baclace
> Priority: Critical
>
> A cluster can be specified with "waves" by supporting an optional suffix on
> whirr.instance-templates property in order to provide *running* base-level
> services (like ZK or a master-master mysql) to another layer of services
> during the configuration phase. This enables storing cluster-wide information
> in zookeeper or doing db creation beforehand.
> An example of a two "wave" (avoiding "phase" which already has a meaning)
> cluster:
> whirr.instance-templates.0=1 zookeeper, 2 zookeeper, 4 noop
> The .0 templates run like normal during "whirr launch-cluster" and then,
> during the same Whirr run, the .1 template is applied as a modification of
> the same cluster so that new host instances are not allocated:
> whirr.instance-templates.1=1 my-master, 2 my-gateway, 4 my-worker
> In the second wave, instance provisioning is inhibited, the
> instance-templates must have the same number of commas and same sequence of
> leading numbers, and a role is only allowed to appear in one wave.
> Here is another example:
> whirr.instance-templates.0=1 mysql-master+zookeeper, 1
> mysql-master+zookeeper,4 noop
> whirr.instance-templates.1=1 hadoop-namenode+hadoop-jobtracker, 1
> hbase-master+hadoop-secondarynn,4
> hadoop-tasktracker+hadoop-datanode+hbase-regionserver
> In the first wave, the two mysql-masters form a multi-master ensemble which
> keeps state information about the setup in the Whirr process (much like
> ZooKeeperCluster.getHosts(cluster) informs services/hbase of the quorum).
> In the second wave, nodes are not allocated
> (BootstrapClusterAction.doAction() is inhibited if instances already exist),
> but all phases for LaunchClusterCommand, including beforeBootstrap() and
> afterBootstrap() callbacks, are executed. If other
> whirr.cli.command.*Command are run, they would see a combined
> whirr.instance-templates that works like normal.
> Obviously, there would be no reason to limit this to 2 waves, but I do not
> expect more than 10 waves to be useful, so the pattern could enable a suffix
> of "\.[0-9]".
> Instead of WHIRR-221 which aims to specify a single global order for service
> startup, the wave format has the advantage that it relies on the implicit
> synchronization barriers at phases already supported by Whirr, the phases
> still run actions within phases in parallel, and state generated by a wave is
> available to later waves.
> Conceptually, this merely splits the whirr.instance-templates into waves of
> (bootstrap,install,configure,start). If no .[0-9] suffixes are present, then
> Whirr would behave just like normal.
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