fix: Revert removal of -Xms JVM option

Logstash has '-Xms1g' set inside 'config/jvm.options', so either -Xms
must be set, or -Xmx must be greater than 1g (which is too high of a
default for docker-elk).

Elastic explicitly recommends setting -Xms and -Xmx to the same value
for Elasticsearch:
  https://www.elastic.co/guide/en/elasticsearch/reference/8.2/advanced-configuration.html#set-jvm-heap-size

README.md

@@ -368,11 +368,13 @@ For example, to increase the maximum JVM Heap Size for Logstash:
 logstash:
 
   environment:
-    LS_JAVA_OPTS: -Xmx1g
+    LS_JAVA_OPTS: -Xms1g -Xmx1g
 ```
 
-When these options are not set, both Elasticsearch and Logstash start with an upper cap of [1/4 of the total host
-memory][jvm-heap] set on the JVM Heap Size.
+When these options are not set:
+
+* Elasticsearch starts with a JVM Heap Size that is [determined automatically][es-heap].
+* Logstash starts with a fixed JVM Heap Size of 1 GB.
 
 ### How to enable a remote JMX connection to a service
 
@@ -416,6 +418,7 @@ See the following Wiki pages:
 
 [booststap-checks]: https://www.elastic.co/guide/en/elasticsearch/reference/current/bootstrap-checks.html
 [es-sys-config]: https://www.elastic.co/guide/en/elasticsearch/reference/current/system-config.html
+[es-heap]: https://www.elastic.co/guide/en/elasticsearch/reference/current/important-settings.html#heap-size-settings
 
 [win-filesharing]: https://docs.docker.com/desktop/windows/#file-sharing
 [mac-filesharing]: https://docs.docker.com/desktop/mac/#file-sharing
@@ -436,5 +439,3 @@ See the following Wiki pages:
 [ls-docker]: https://www.elastic.co/guide/en/logstash/current/docker-config.html
 
 [upgrade]: https://www.elastic.co/guide/en/elasticsearch/reference/current/setup-upgrade.html
-
-[jvm-heap]: https://docs.oracle.com/en/java/javase/18/gctuning/parallel-collector1.html#GUID-74BE3BC9-C7ED-4AF8-A202-793255C864C4

docker-compose.yml

@@ -36,7 +36,7 @@ services:
       - "9200:9200"
       - "9300:9300"
     environment:
-      ES_JAVA_OPTS: -Xmx512m
+      ES_JAVA_OPTS: -Xms512m -Xmx512m
       # Bootstrap password.
       # Used to initialize the keystore during the initial startup of
       # Elasticsearch. Ignored on subsequent runs.
@@ -61,7 +61,7 @@ services:
       - "5000:5000/udp"
       - "9600:9600"
     environment:
-      LS_JAVA_OPTS: -Xmx256m
+      LS_JAVA_OPTS: -Xms256m -Xmx256m
       LOGSTASH_INTERNAL_PASSWORD: ${LOGSTASH_INTERNAL_PASSWORD:-}
     networks:
       - elk

extensions/enterprise-search/enterprise-search-compose.yml

@@ -9,7 +9,7 @@ services:
     volumes:
       - ./extensions/enterprise-search/config/enterprise-search.yml:/usr/share/enterprise-search/config/enterprise-search.yml:ro,Z
     environment:
-      JAVA_OPTS: -Xmx2g
+      JAVA_OPTS: -Xms2g -Xmx2g
       ENT_SEARCH_DEFAULT_PASSWORD: 'changeme'
       ELASTIC_PASSWORD: ${ELASTIC_PASSWORD:-}
     ports: