[prod] Geographically spread hosts

[jakubgs]

If we use Elastic Load Balancers we can spread the Elastic Beanstalk host across multiple geographical locations. Affects #1.

[jakubgs]

There is a setting in the CloudPosse module module that can do this:

• availability_zones - Choose the number of AZs for your instances.

https://github.com/cloudposse/terraform-aws-elastic-beanstalk-environment/blob/01d405201c192ee1948ea97bff6742140b1cfbba/variables.tf#L232-L235

But that's only within one region. I don't think I can easily do geographical load balancing with just ELBs. For that I'd need Route 53, but I can't use it because it doesn't support the .ps TLD.

[jakubgs]

The issue with geographically spreading EB environments is that they still would share the storage(MongoDB), which would have to be in one geographical location, with possibly read-only replicas in other regions. Though that has the possibility of showing outdated state, though in our case with low writes it could be fine.

This could be achieved through a sharded cluster:

• https://docs.mongodb.com/manual/tutorial/deploy-shard-cluster/index.html
• https://docs.mongodb.com/manual/reference/glossary/#term-sharded-cluster
• https://docs.mongodb.com/manual/core/sharded-cluster-components/

This could work, though usually these kinds of clusters depend on being able to shard data depending on where from it's mostly accessed, which isn't relevant to our use case.

This kind of sharded cluster setup would also require at least 3 hosts in each region for reliability, which would greatly increase costs.