My WordPress/MySQL Docker instances on AWS are unhappy: after some time, they stop. No idea why. All I see is
Failed Units: 1 polkit.service
when I log in after WordPress seems to have died. And no Docker process is running. While I can restart them easily, it’s annoying to do so manually. At this point I have 2 possibilities: find the root cause, or work around it via monitoring and automatic restarting when needed.
And a load balancer to make the service available even when AWS does kill my Docker containers would be nice. Actually a load balancer has to do monitoring anyway. Since this topic came up at work too, it’s double useful. So a load balancer it is!
A nice article, although a bit dated, is here. He knows what he’s talking about: he made up elastic binary trees and wrote haproxy and made it saturate a 10G link back in 2009.
nginx is a popular http load balancer (amond other things it can do), but since haproxy can do TCP in general, it’s more universally suitable for me, so that’s what it’ll be.
Step 1 is to have something to load balance. Because this is blog runs on WordPress with its MySQL instance, doubling this is non-trivial: WordPress keeps files in its web directory, and the MySQL instanced would need a multi-master replication setup.
Instead I’ll have a static copy of the web page…and then use a load balancer to switch to the static page when the primary is dead.
PS: To be fair AWS might not be at fault here. Truth is: I don’t know what’s causing the problem. On Google Cloud I had no such issue, but that’s about all I can say. I don’t expect problems in the Docker containers as they are quite literally identical. Even the version of CoreOS is identical.
Anyway, this all sounds like a good excuse to set up some load balancing and monitoring.