How to fix ElasticSearch [1]: initial heap size [...] not equal to maximum heap size [...];

Problem:

Your ElasticSearch server fails to start with an error message like

ERROR: [1] bootstrap checks failed
[1]: initial heap size [536870912] not equal to maximum heap size [2147483648]; this can cause resize pauses and prevents memory locking from locking the entire heap
ERROR: Elasticsearch did not exit normally - check the logs at /usr/share/elasticsearch/logs/docker-cluster.log

Solution

Set the initial heap size equal to the maximum heap size: The -Xms argument and the -Xmx argument must be equal, for example:

-Xms2048m -Xmx2048m

Typically (such as in a docker-based setup) you can set this in ES_JAVA_OPTS:

ES_JAVA_OPTS=-Xms2048m -Xmx2048m

For docker-compose based environments, this is an example configuration that works:

environment:
    - cluster.name=docker-cluster
    - node.name=elasticsearch1
    - cluster.initial_master_nodes=elasticsearch1
    - bootstrap.memory_lock=true
    - http.cors.allow-origin=http://localhost:1358,http://127.0.0.1:1358
    - http.cors.enabled=true
    - http.cors.allow-headers=X-Requested-With,X-Auth-Token,Content-Type,Content-Length,Authorization
    - http.cors.allow-credentials=true
    - "ES_JAVA_OPTS=-Xms2048m -Xmx2048m"

After that, restart your ElasticSearch instance.