🐛 Set timezone to Europe/London (successfully, this time)

[sldblog]

What does this pull request do?

This PR fixes a 🐛 about setting the timezone to Europe/London in the Docker build.

As part of a set of conversations with @mahalrmoj we've discovered that the UI app is currently running on UTC:

$ k exec -ti hmpps-interventions-ui-5fc67cffcd-z4kgx --namespace=hmpps-interventions-dev -- date
Thu Apr  8 14:48:13 UTC 2021

How?

• b6dc7cb adds a "build-time test" -- verifies that the timezone file in fact exists
• 774f922 then installs the package that provides that timezone file

Result:

$ docker build --tag=ui .
...<snip>...

$ docker run --rm -ti ui date
Thu Apr  8 15:47:44 BST 2021

What is the intent behind these changes?

To make sure the service is running in Europe/London timezone. It has no material impact on our APIs, but it's the least surprising default :) -- At least it doesn't look like we're setting the timezone when we aren't.

[sldblog]

Instead of this line, we could also add a "docker build test" that would test the timezone by running the date command:

$ docker run --rm -ti <built_tag> date | egrep "(GMT|BST)"
Thu Apr  8 15:55:29 BST 2021
# exit status 0

vs

$ k exec -ti hmpps-interventions-ui-5fc67cffcd-z4kgx -- date | egrep "(GMT|BST)"
# exit status 1, thus failing the build

However, this isn't trivial to chain after the docker build, before the push at the moment

[lawrence-forooghian]

What impact does this have on the application? Do you have an example of how the container's time zone is affecting its behaviour?

Edit: I guess that from this you mean it doesn't affect the UI app?

It has no material impact on our APIs

[tomsmyers]

without properly understanding the context - it doesn't seem appropriate to rely on the TZ of the container for anything at all. we have libraries already in use in this repo that allow formatting in whatever TZ you like. e.g.

    const ukDate = getZonedTime(date, findTimeZone('Europe/London'))

[sldblog]

Apologies, I skimmed over a few important points

1. The most important bit is fixing the false promise of the Dockerfile: it sets TZ to London, so if it does that, that should work.
2. The second is that the service inherited this setting from the Kotlin template and it bothers my sense of consistency. It does have a suggestion open to switch to UTC by default. (Consider changing default timezone to UTC hmpps-template-kotlin#29)
3. Distant third (I'm not precious about this) is what we get back from the "now" instant. We're deployed in the London region, not having to work in other countries, so it can be the same time we see on the clock. This is really minor though.

I'm perfectly happy to switch this to be explicitly UTC (and open a similar in the service) -- what do you prefer?

[tomsmyers]

agree with your comments david. we shouldn't rely on this, but setting it correctly can't be a bad thing.