Use dartsass for publisher css compilation

[mtaylorgds]

What

Change docker compose for Mainstream Publisher to match compilation of CSS using dart-sass. See alphagov/publisher#2278.

Why

We're switching these apps from libsass to dart-sass, and this change is needed to support that.

[kevindew]

Something that is a bit weird about this approach (and appreciate horse has bolted for a bunch of our repos) is that bin/dev is going to be managing multiple processes which isn't typical behaviour for docker. It raises quite a wtf for apps like this where there is also a worker process - why have that managed differently in docker to css?

We should also manage all dev processes from the Procfile so the worker process should also be defined there, not just web and css.

I'd suggest you take the approach we've done in govuk-chat and have each individual process be it's own docker process:

govuk-docker/projects/govuk-chat/docker-compose.yml

Lines 50 to 54 in 9604d0b

	command: bin/dev web
	govuk-chat-css:
	<<: *govuk-chat
	command: bin/dev css

[davidtrussler]

I have tried this approach locally and found that it does not run Sass in watch mode (as described here). I don't know if that is inherent in the approach or if it requires a change in this file to run.

[kevindew]

it will be running the exact same process

[davidtrussler]

What I am seeing in the console as I start publisher is shown below, comparing the original changes with what is suggested here, which suggests the command Execute dartsass:watch is not being called. I guess that will require some changes in the config in Publisher as well.

[kevindew]

For the latter you need to execute publisher-css as a separate process and/or flag it as a dependency of the process - as per how the worker is configured,

govuk-docker/projects/publisher/docker-compose.yml

Line 39 in 9fbfaea

- publisher-worker

The former example you've got there is unconventional for docker as it's managing 2 processes

[davidtrussler]

OK, that's making sense (and also working as expected 😄) so I have updated accordingly.

[kevindew]

Great 😄 you'll just need to edit:

govuk-docker/projects/publisher/docker-compose.yml

Lines 33 to 39 in 1de6d85

	depends_on:
	- redis
	- mongo-3.6
	- nginx-proxy
	- publishing-api-app
	- link-checker-api-app
	- publisher-worker

to include publisher-css, which will mean that css is automatically started when web is started.

[davidtrussler]

Oh yeah, have done that as well. 👍