This is for internal use by the PaaS team. Public-facing documentation is located at docs.cloud.service.gov.uk.

ADR0053: Plan for maintaining product pages post Ireland retirement

Context

The PaaS product pages is a static site that is currently deployed to GitHub pages accessible at both www.cloud.service.gov.uk and cloud.service.gov.uk.

The current DNS configuration in Route 53 has a CNAME record for www.cloud.service.gov.uk which points to GitHub’s servers and a CNAME record for cloud.service.gov.uk which points to the load balancer in the Ireland region.

A user that navigates to cloud.service.gov.uk is redirected to www.cloud.service.gov.uk as traffic for that domain is passed from the load balancer in the Ireland region via the GoRouter to an app which performs an HTTP redirect. The app is a nginx application that is currently deployed to the Ireland region with a route that maps to cloud.service.gov.uk.

However once the Ireland region is decommissioned we will still need to perform an HTTP redirect from cloud.service.gov.uk to www.cloud.service.gov.uk. There are several ways of doing this.

Options

Option 1: CDN

This involves hosting a custom CDN instance using Amazon CloudFront as outlined in our documentation.

Since cloud.service.gov.uk is an apex domain we cannot set a CNAME record nor do we know the IP addresses for the CDN instance up front. However, Amazon Route 53 provides a feature known as ‘alias’ records which are an extension to DNS that allows traffic to be directed to AWS resources. This allows the DNS query for cloud.service.gov.uk to resolve to the IP address of the CDN instance.

The paas-product-pages-redirect app will have to be deployed to the PaaS London region accessible at paas-product-pages-redirect.london.cloudapps.digital. The CDN instance will then need to be configured to modify the incoming Host header to paas-product-pages-redirect.london.cloudapps.digital. This allows the GoRouter to send the request to the redirect app.

Option 2: ALB redirect

This involves creating an A record for cloud.service.gov.uk that points to the load balancer in the London region with a HTTP/s listener rule that performs an HTTP redirect to www.cloud.service.gov.uk.

Since the HTTP redirect is done by the load balancer the redirect app is unnecessary and can be deleted.

Option 3: Private domain

This involves creating an A record for cloud.service.gov.uk that points to the load balancer in the London region with cloud.service.gov.uk added to the Cloud Foundry deployment as a new private domain.

The paas-product-pages-redirect app will be deployed in the London region accessible at paas-product-pages-redirect.london.cloudapps.digital with a route that maps to cloud.service.gov.uk.

Option 4: DNS

This involves creating several A records for cloud.service.gov.uk that point towards the IP addresses for GitHub’s servers outlined here.

Since both the wwww and apex domains resolve to GitHub’s servers the redirect app is unnecessary and can be deleted.

Decision

Consensus team decision is Option 4 as it involves only a DNS change. Since there are other DNS records (e.g. DMARC, etc…) for the cloud.service.gov.uk domain that need to be kept it makes sense to just make DNS changes in the Terraform.

Status

Accepted

Consequences

Users will be able to continue to access the product pages at cloud.service.gov.uk.