juju deploy tags are persistent accross juju deploys

[Dave Chiluk]

Testcase
Create a single machine in maas, and assign the tag "bootstrap" to it.
$ juju bootstrap --upload-tools --show-log --debug --constraints tags=bootstrap
$ juju deploy mysql
ubuntu@maas:~⟫ juju status
environment: maas
machines:
  "0":
    agent-state: started
    agent-version: 1.21.3.1
    dns-name: bootstrap01.maas
    instance-id: /MAAS/api/1.0/nodes/node-57b83994-ccce-11e4-aec3-52540027b454/
    series: trusty
    hardware: arch=amd64 cpu-cores=2 mem=2048M tags=virtual,bootstrap,bootstrap01
    state-server-member-status: has-vote
  "1":
    agent-state-info: 'cannot run instances: cannot run instances: gomaasapi: got
      error back from server: 409 CONFLICT (No available node matches constraints:
      tags=bootstrap zone=default)'
    instance-id: pending
    series: trusty
services:
  mysql:
    charm: cs:trusty/mysql-23
    exposed: false
    relations:
      cluster:
      - mysql
    units:
      mysql/0:
        agent-state: pending
        machine: "1"

Mysql fails to deploy because it can't find another node with the bootstrap tag.

[Dave Chiluk (chiluk)]

Juju deployed from ppa:juju/stable
ii juju 1.21.3-0ubuntu1~14.04.1~juju1 all next generation service orchestration system
ii juju-core 1.21.3-0ubuntu1~14.04.1~juju1 amd64 Juju is devops distilled - client
ii juju-deployer 0.4.3-0ubuntu1~ubuntu14.04.1~ppa1 all Deploy complex stacks of services using Juju
ii python-jujuclient 0.50.1-2 amd64 Python API client for juju-core

[Ian Booth (wallyworld)]

Hey Dave, what you are seeing is Juju working as designed:

when you specify constraints at bootstrap time, these become the default constraints to use (unless otherwise specified) for all subsequent machine deploys. These are called "environment constraints".

For MAAS, tags are most commonly used when choosing machines on which to deploy charms and thus apply for that service only. Or if a tag is used at bootstrap time, it will be used for a cluster of machines tagged as being available for that environment, so that subsequent deploys all use the same tag.

For your use case, that's not normally how MAAS would be set up - as stated above, a number of machines would be tagged. So what you would need to do after bootstrap is adjust the environment constraints:

juju set-constraints tags=

(I think the above works, never done it with empty tags before).

I think there's a usability issue here, rather than a bug as such. I'll re-triage to Medium.