Handle mismatched spaces

[David Ames]

While testing converged networking I hit the following with nova-cloud-controller:

subprocess.CalledProcessError: Command '['nova-manage', 'cell_v2', 'map_cell0']' returned non-zero exit status 255.

The issue was mismatched spaces:

  nova-cloud-controller:
    bindings:
      "": *public-space
      public: public
      internal: internal
      admin: admin

  nova-mysql-router:
    bindings:
      "": *public-space
      db-router: internal

This resulted in the mysql-router using the internal space for db-router but the implicit shared-db binding for nova-cloud-controller used the default: *public-space.

This led to a mismatch of which address was expected:

juju-exec nova-mysql-router/0 -- "relation-get -r db-router:53 - nova-mysql-router/0"
egress-subnets: 172.16.200.14/32
ingress-address: 172.16.200.14
mysqlrouter_hostname: 172.16.200.14
mysqlrouter_username: mysqlrouteruser
nova_database: nova
nova_hostname: 192.168.151.96
nova_username: nova
novaapi_database: nova_api
novaapi_hostname: 192.168.151.96
novaapi_username: nova
novacell0_database: nova_cell0
novacell0_hostname: 192.168.151.96
novacell0_username: nova
private-address: 172.16.200.14

This happens because proxy_db_and_user_requests blindly repeats what it receives over the shared-db relation (from the client) to the db-router relation (to the server).

We may want the mysql-router charm to intervene and force the *_hostname values to the bound db-router IP.

WORKAROUND:

Explicitly set nova-cloud-controller's (and potentially others') shared-db to the same binding the nova-cloud-controller-mysql-router's db-router is bound to. i.e.

  nova-cloud-controller:
    bindings:
      "": *public-space
      public: public
      internal: internal
      admin: admin
      shared-db: internal

  nova-mysql-router:
    bindings:
      "": *public-space
      db-router: internal

[David Ames (thedac)]

After discussing with the team, having the subordinate force the binding of the primary charm seems incorrect.

Therefore, this is now a documentation bug.

In general the following bindings need to be on the same space:

mysql-innodb-cluster: db-router and cluster bindings
mysql-router: db-router binding
primary charm: shared-db

i.e. All of these bindings use the "internal" binding bellow:

  nova-cloud-controller:
    bindings:
      "": *public-space
      public: public
      internal: internal
      admin: admin
      shared-db: internal

  nova-mysql-router:
    bindings:
      "": *public-space
      db-router: internal

  mysql-innodb-cluster:
    "": *public-space
    db-router: internal
    cluster: internal

[Peter Matulis (petermatulis)]

The documentation aspect was fixed in the READMEs for both the mysql-router and mysql-innodb-cluster charms.