Fastly config for mobile backend

[jflm]

Have tried to keep the config simple as it's a very straightforward use case. Rather than putting values in govuk-fastly-secrets (as I don't think we have any secret values currently) I've just set config vars in Terraform directly. But if we're not happy with this approach I can change it.

I've also opted not to use a custom VCL as I think we can achieve everything we need to just by declaring it in TF. But I am pretty new at Fastly so again definitely will appreciate thoughts and views.

In order for this to work, assume we will also need to make some changes in govuk-dns-tf which I'll have a look at now.

[samsimpson1]

FYI using a *.gov.uk domain will cause the service creation to fail because Fastly requires manual approval to use gov.uk domains. You'll have to create a support ticket with them to get them to add the domains you want to the whitelist.

[theseanything]

Do you know if we have to create a service (i.e. with placeholder hostname) before contacting them?

[jflm]

Yep turns out this ☝🏼 is correct - have updated the PR to include placeholder hostnames (on top of *.govuk.digital) so we can provide the service IDs to Fastly support

[samsimpson1]

I've made some changes to the structure of the TF files in this PR since I made some structural changes to this repo yesterday.

This looks good to me, I've also created a PR in govuk-fastly-secrets which will be required to create the TFC workspace for the new service.

When you're ready, merge this PR in first then the govuk-fastly-secrets one.