Fix broken elasticsearch configuration

Because we are running a version of elasticsearch older than Methusalem,
the docker environment variables were not properly taken into account.
For instance, the cluster name and "mlockall" settings were incorrect,
as we could see by running:

    $ tutor local run lms curl elasticsearch:9200 | grep cluster_name
    ...
      "cluster_name" : "elasticsearch",
    $ tutor local run lms curl elasticsearch:9200/_nodes/process?pretty | grep mlock
      ...
     "mlockall" : false

See
https://discuss.overhang.io/t/elastic-container-is-not-being-removed/312/3
for discussion.

This fix also introduces a new tutor configuration setting to adjust the
elasticsearch heap size.

CHANGELOG.md

@@ -4,6 +4,8 @@ Note: Breaking changes between versions are indicated by "💥".
 
 ## Unreleased
 
+- [Improvement] Make it possible to configure the elasticsearch heap size
+- [Bugfix] Fix broken elasticsearch environment variables
 - [Improvement] Restore more recent Android app version (#289).
 
 ## v3.11.4 (2020-02-16)

docs/configuration.rst

@@ -115,6 +115,7 @@ Elasticsearch
 
 - ``ELASTICSEARCH_HOST`` (default: ``"elasticsearch"``)
 - ``ELASTICSEARCH_PORT`` (default: ``9200``)
+- ``ELASTICSEARCH_HEAP_SIZE`` (default: ``"1g"``)
 
 Memcached
 *********

tutor/templates/config.yml

@@ -43,6 +43,7 @@ DOCKER_REGISTRY: "docker.io/"
 LOCAL_PROJECT_NAME: "tutor_local"
 ELASTICSEARCH_HOST: "elasticsearch"
 ELASTICSEARCH_PORT: 9200
+ELASTICSEARCH_HEAP_SIZE: 1g
 FORUM_HOST: "forum"
 JWT_COMMON_AUDIENCE: "openedx"
 JWT_COMMON_ISSUER: "{% if ACTIVATE_HTTPS %}https{% else %}http{% endif %}://{{ LMS_HOST }}/oauth2"

tutor/templates/local/docker-compose.yml

@@ -35,10 +35,7 @@ services:
   {% if ACTIVATE_ELASTICSEARCH %}
   elasticsearch:
     image: {{ DOCKER_REGISTRY }}{{ DOCKER_IMAGE_ELASTICSEARCH }}
-    environment:
-      - "ES_JAVA_OPTS=-Xms1g -Xmx1g"
-      - "cluster.name=openedx"
-      - "bootstrap.memory_lock=true"
+    command: ["elasticsearch", "-Xms{{ ELASTICSEARCH_HEAP_SIZE }}", "-Xmx{{ ELASTICSEARCH_HEAP_SIZE }}", "--cluster.name=openedx", "--bootstrap.mlockall=true"]
     ulimits:
       memlock:
         soft: -1