Implement PLATFORM_RELATIONSHIPS, fixes #9

[rfay]

• PLATFORM_RELATIONSHIPS environment variable and mapping .platform.app.yaml and services.yaml #9

This implements PLATFORM_RELATIONSHIPS with local DDEV-based values.

• mariadb/mysql/postgres
• elasticsearch
• redis
• memcached

This can be tested with

ddev get https://github.com/rfay/ddev-platformsh/tarball/20221024_platform_relationships

TODO:

• The scripts to generate relationships should go into a gitignored directory.

[rfay]

Works OOTB on https://github.com/symfonycorp/platformsh-symfony-template.git@symfony-6.1-php8.1-webapp

[lolautruche]

Is this an fixed IP in DDEV or just dummy? (same question for the other services below)

[rfay]

This is dummy. I'm hoping nothing uses it. It would be better as an obvious dummy, like 255.255.255.255. If it's actually used, we would have to figure it out at ddev start time instead of here, which may be what we want anyway. So worth considering moving all this generation to ddev start time.

[rfay]

It also would be reasonable to put hostname here, but not sure if that would break something. Changed this to use 255.255.255.255 for now.

[lolautruche]

Thanks for the clarification. We can't use a hostname here, since we have a dedicated hostname property.
We'll probably need to indeed figure it out at ddev start, but this may be a follow-up task.
WDYT @gilzow ?

[lolautruche]

Can the services (DB, elasticsearch, memcached, redis) change e.g. the port they expose?

[lolautruche]

This is great!
However, I wonder why you removed the platform.yaml provider.

[rfay]

DDEV automatically provides platform.yaml (and has for several months). It's the version that was originally developed for the add-on. And ddev start overwrites it anyway with DDEV's own version.