Kubernetes, Docker and vm.max_map_count

While attempting to run ElasticSearch on K8 I ran into an error that would kill the container:

max virtual memory areas vm.max_map_count [65530] is too low, increase to at least [262144]

Fortunately this is pretty well documented and I was able to figure out a configuration setting for the container that got it stable. This question isn't about that.

The question that arises for me is why does this happen on K8 versus Docker? I'm using the same image (The official ES image) in both cases so what are some of the reasons why the value would be different? Is there a way I could configure K8 or the machines I'm running it on so that this situation wouldn't arise?

The setting for vm.max_map_count can be changed on the host level. Your can read the current value like this: sysctl vm.max_map_count. To change it run: sudo sysctl -w vm.max_map_count=262144. This will be reverted by the next boot. To set it permanently add vm.max_map_count=262144 to /etc/sysctl.conf.

Most Elasticsearch setups for Kubernetes use an Init Container to make sure this value is set like required. The drawback here is that it needs to in privileged mode: Elasticsearch Helm Chart

It is also possible to set sysctls in the securityContext of a Pod. But for now virtual memory settings are considered unsafe and need some more tweaking on your Kubernetes setup.