Set ELK components version from .env file

Closes #189

.env

@@ -0,0 +1 @@
+ELK_VERSION=5.6.3

README.md

@@ -42,6 +42,8 @@ Based on the official Docker images:
 6. [JVM tuning](#jvm-tuning)
    * [How can I specify the amount of memory used by a service?](#how-can-i-specify-the-amount-of-memory-used-by-a-service)
    * [How can I enable a remote JMX connection to a service?](#how-can-i-enable-a-remote-jmx-connection-to-a-service)
+7. [Updates](#updates)
+   * [Using a newer stack version](#using-a-newer-stack-version)
 
 ## Requirements
 
@@ -57,7 +59,7 @@ On distributions which have SELinux enabled out-of-the-box you will need to eith
 into Permissive mode in order for docker-elk to start properly. For example on Redhat and CentOS, the following will
 apply the proper context:
 
-```bash
+```console
 $ chcon -R system_u:object_r:admin_home_t:s0 docker-elk/
 ```
 
@@ -67,13 +69,13 @@ $ chcon -R system_u:object_r:admin_home_t:s0 docker-elk/
 
 Start the ELK stack using `docker-compose`:
 
-```bash
+```console
 $ docker-compose up
 ```
 
 You can also choose to run it in background (detached mode):
 
-```bash
+```console
 $ docker-compose up -d
 ```
 
@@ -94,7 +96,7 @@ By default, the stack exposes the following ports:
 Now that the stack is running, you will want to inject some log entries. The shipped Logstash configuration allows you
 to send content via TCP:
 
-```bash
+```console
 $ nc localhost 5000 < /path/to/logfile.log
 ```
 
@@ -117,7 +119,7 @@ about the index pattern configuration.
 
 Run this command to create a Logstash index pattern:
 
-```bash
+```console
 $ curl -XPUT -D- 'http://localhost:9200/.kibana/index-pattern/logstash-*' \
     -H 'Content-Type: application/json' \
     -d '{"title" : "logstash-*", "timeFieldName": "@timestamp", "notExpandable": true}'
@@ -125,8 +127,8 @@ $ curl -XPUT -D- 'http://localhost:9200/.kibana/index-pattern/logstash-*' \
 
 This command will mark the Logstash index pattern as the default index pattern:
 
-```bash
-$ curl -XPUT -D- 'http://localhost:9200/.kibana/config/5.6.2' \
+```console
+$ curl -XPUT -D- 'http://localhost:9200/.kibana/config/5.6.3' \
     -H 'Content-Type: application/json' \
     -d '{"defaultIndex": "logstash-*"}'
 ```
@@ -259,3 +261,18 @@ logstash:
   environment:
     LS_JAVA_OPTS: "-Dcom.sun.management.jmxremote -Dcom.sun.management.jmxremote.ssl=false -Dcom.sun.management.jmxremote.authenticate=false -Dcom.sun.management.jmxremote.port=18080 -Dcom.sun.management.jmxremote.rmi.port=18080 -Djava.rmi.server.hostname=DOCKER_HOST_IP -Dcom.sun.management.jmxremote.local.only=false"
 ```
+
+## Updates
+
+### Using a newer stack version
+
+To use a different Elastic Stack version than the one currently available in the repository, simply change the version
+number inside the `.env` file, and rebuild the stack with:
+
+```console
+$ docker-compose build
+$ docker-compose up
+```
+
+**NOTE**: Always pay attention to the [upgrade instructions](https://www.elastic.co/guide/en/elasticsearch/reference/current/setup-upgrade.html)
+for each individual component before performing a stack upgrade.

docker-compose.yml

@@ -3,7 +3,10 @@ version: '2'
 services:
 
   elasticsearch:
-    build: elasticsearch/
+    build:
+      context: elasticsearch/
+      args:
+        ELK_VERSION: $ELK_VERSION
     volumes:
       - ./elasticsearch/config/elasticsearch.yml:/usr/share/elasticsearch/config/elasticsearch.yml
     ports:
@@ -15,7 +18,10 @@ services:
       - elk
 
   logstash:
-    build: logstash/
+    build:
+      context: logstash/
+      args:
+        ELK_VERSION: $ELK_VERSION
     volumes:
       - ./logstash/config/logstash.yml:/usr/share/logstash/config/logstash.yml
       - ./logstash/pipeline:/usr/share/logstash/pipeline
@@ -29,7 +35,10 @@ services:
       - elasticsearch
 
   kibana:
-    build: kibana/
+    build:
+      context: kibana/
+      args:
+        ELK_VERSION: $ELK_VERSION
     volumes:
       - ./kibana/config/:/usr/share/kibana/config
     ports:

elasticsearch/Dockerfile

@@ -1,5 +1,7 @@
+ARG ELK_VERSION
+
 # https://github.com/elastic/elasticsearch-docker
-FROM docker.elastic.co/elasticsearch/elasticsearch:5.6.3
+FROM docker.elastic.co/elasticsearch/elasticsearch:${ELK_VERSION}
 
 # Add your elasticsearch plugins setup here
 # Example: RUN elasticsearch-plugin install analysis-icu

kibana/Dockerfile

@@ -1,5 +1,7 @@
+ARG ELK_VERSION
+
 # https://github.com/elastic/kibana-docker
-FROM docker.elastic.co/kibana/kibana:5.6.3
+FROM docker.elastic.co/kibana/kibana:${ELK_VERSION}
 
 # Add your kibana plugins setup here
 # Example: RUN kibana-plugin install <name|url>

logstash/Dockerfile

@@ -1,5 +1,7 @@
+ARG ELK_VERSION
+
 # https://github.com/elastic/logstash-docker
-FROM docker.elastic.co/logstash/logstash:5.6.3
+FROM docker.elastic.co/logstash/logstash:${ELK_VERSION}
 
 # Add your logstash plugins setup here
 # Example: RUN logstash-plugin install logstash-filter-json