Docker compose links flag is deprecated, but still used

[tmotyl]

What happened (or feature request):

According to the docker documentation "links" flag is deprecated. It is still used in ddev composer yaml
e.g.

web:
    links:
      - db:db

https://docs.docker.com/compose/compose-file/#links

[rfay]

Color me surprised; I tried to just remove those links stanzas because https://docs.docker.com/compose/compose-file/#links basically says they're not useful.

But things blow up in quite surprising ways; it looks like other projects' db servers are being hit randomly. So a Drupal install starts but fails partway through, it hits "variable table already exists", implying that it is suddenly hitting the wrong "db" container.

The doc says:

Links are not required to enable services to communicate - by default, any service can reach any other service at that service’s name.

So it seems there would be no reason for the stanza at all. But it seems there is. Things work perfectly when it's reintroduced.

[rfay]

This is a totally valid issue, but I don't think it's going to be worth pursuing until we're forced to pursue it, so flagging hibernate.

[rfay]

There may be a docker bug here.

People have been having trouble with solr being accidentally shared between projects, and removing links from this solr recipe does not solve that problem:

https://github.com/drud/ddev/blob/1bdcde384c610b3b17834585b1292580fdafe299/pkg/servicetest/testdata/services/docker-compose.solr.yaml#L63-L68

[rfay]

As of v1.19, the links: stanza is no longer used. Thanks for this issue!