Hi all,
I'm pleased to say that availability zone support for AWS and OpenStack has
now landed on trunk, and will be available in 1.19.4. I'll write a blog
post and maybe even some docs about it, but for now here's a brief
description how you can use this feature.
FYI: not all OpenStacks are created equal. Yours may not support
availability zones. HP's revamped HP Cloud offering does offer several
availability zones in the US West region.
Explicit AZs
=========
When bootstrapping or adding a machine, you can specify the availability
zone explicitly as a placement directive. e.g.
juju bootstrap --to zone=us-east-1b
juju add-machine zone=us-east-1c
Automatic AZ spread
================
TL;DR: "juju deploy -n 10 <service>" will automatically and uniformly
distribute the units to instances spread across the AZs within the region.
Assuming the charm and service being charmed is well written, then you
should be able to rest assured that IaaS downtime will not affect your
application.
When adding machines without an AZ explicitly specified, or when adding
units to a service, the ec2 and openstack providers will now automatically
spread instances across all available AZs in the region. The spread is
based on density of instance "distribution groups".
State servers compose a distribution group: when doing "juju
ensure-availability", state servers will be spread across AZs. Each
deployed service (e.g. mysql, redis, whatever) composes a separate
distribution group; the AZ spread of one service does not affect the AZ
spread of another service.
Cheers,
Andrew
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