在单个主机上运行多节点Elasticsearch集群是否有意义？

Question

What do I get by running multiple nodes on a single host? I am not getting availability, because if the host is down, the whole cluster goes with it. Does it make sense regarding performance? Doesn't one instance of ES take as many resources from the host as it needs?

Answer 1

It depends on your host and how you configure your nodes.

For example, Elastic recommends allocating up to 32GB of RAM (because of how Java compresses pointers) to elasticsearch and have another 32GB for the operating system (mostly for disk caching).

Assuming you have more than 64GB of ram on your host, let's say 128, it makes sense to have two nodes running on the same machine, having both configured to 32GB ram each and leaving another 64 for the operating system.

Answer 2

Generally no, but if you have machines with ridiculous amounts of CPU and memory, you might want that to properly utilize the available resources. Avoiding big heaps with Elasticsearch is a good thing generally since garbage collection on bigger heaps can become a problem and in any case above 32 GB you lose the benefit of pointer compression. Mostly you should not need big heaps with ES. Most of the memory that ES uses is through memory mapped files, which relies on the OS cache. So just because you aren't assigning memory to the heap doesn't mean it is not being used: more memory available for caching means you'll be able to handle bigger shards or more shards.

So if you run more nodes, that advantage goes away and you waste memory on redundant heaps, and you'll have nodes competing for resources. Mostly, you should base these decisions on actual memory, cache, and cpu usage of course.