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Docker Websocket Chat Sample

We’ve decided to use docker containers to package and deploy application components as nano services. This post documents initial experimentation to build and run a sample application as a service.

The application is a spring integration stomp over websockets chat sample app. It is a java application running in an embedded tomcat container, packaged as a stanadalone (uber) jar.

This type of application seems to be a great fit for a docker container

  • self-contained; includes dependencies
  • provides a service
  • consists of one process
  • can be used by other services (or people but we’ll pretend it’s a messaging service for our applications)

install docker

I’m using OS X so I used the installation instructions found here. Be sure to do the boot2docker bit.

Use whatever is appropriate for your OS.

get application code

I’m using Spring integration samples from here. I cloned the git repo locally using

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git clone git@github.com:spring-projects/spring-integration-samples.git ~/spring-integration-samples

Modify the index.html a bit so the host:port are not hard-coded:

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diff --git a/applications/stomp-chat/src/main/resources/static/index.html b/applications/stomp-chat/src/main/resources/static/index.html
index 9add0e0..2e99b6e 100644
--- a/applications/stomp-chat/src/main/resources/static/index.html
+++ b/applications/stomp-chat/src/main/resources/static/index.html
@@ -1,8 +1,8 @@
 <html>
 <head>
     <title>WebSocket Chat</title>
-    <script src="http://localhost:8080/sockjs.js"></script>
-    <script src="http://localhost:8080/stomp.js"></script>
+    <script src="/sockjs.js"></script>
+    <script src="/stomp.js"></script>
     <script type="text/javascript">

         var sock, stompClient, currentUser, subscriptions = {};
@@ -11,7 +11,7 @@
             var userValue = document.getElementById('user');
             if (userValue.value != "") {
                 currentUser = userValue.value;
-                sock = new SockJS('http://localhost:8080/chat');
+                sock = new SockJS('/chat');
                 stompClient = Stomp.over(sock);

run code locally

from ~/spring-integration-samples directory run

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./gradlew stomp-chat:run

using a browser point to http://localhost:8080/ and play with the app.

build uber jar

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./gradlew stomp-chat:build

will build and test the app.

The file we will use is applications/stomp-chat/build/libs/stomp-chat-3.0.0.BUILD-SNAPSHOT.jar

build docker image

Make new empty directory for the Dockerfile and context (files destined for image) and copy the jar file there.

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mkdir ~/docker-chat; cd $_
cp ~/spring-integration-samples/applications/stomp-chat/build/libs/stomp-chat-3.0.0.BUILD-SNAPSHOT.jar .
Dockerfile

create Dockerfile and populate with these lines:

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FROM dockerfile/java:oracle-java7
ADD stomp-chat-3.0.0.BUILD-SNAPSHOT.jar /app/
EXPOSE 8080
ENTRYPOINT ["/usr/bin/java", "-jar", "/app/stomp-chat-3.0.0.BUILD-SNAPSHOT.jar"]

Those instructions tell docker to

  • use a base image that has java installed
  • copy our jar file into the /app directory (creating the directory if needed)
  • make port 8080 available for mapping
  • execute the jar file when the container is started
create docker image

On OS X I need to point at my docker vm to communicate with the daemon. I can get the necessary environment variable exports using

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boot2docker shellinit
Writing /Users/mfrasier/.boot2docker/certs/boot2docker-vm/ca.pem
Writing /Users/mfrasier/.boot2docker/certs/boot2docker-vm/cert.pem
Writing /Users/mfrasier/.boot2docker/certs/boot2docker-vm/key.pem
    export DOCKER_HOST=tcp://192.168.59.103:2376
    export DOCKER_CERT_PATH=/Users/mfrasier/.boot2docker/certs/boot2docker-vm
    export DOCKER_TLS_VERIFY=1

Copy the export commands and paste in shell to execute.

Build the image
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docker build -t mfrasier/stomp-chat .
Sending build context to Docker daemon 56.79 MB
Sending build context to Docker daemon
Step 0 : FROM dockerfile/java:oracle-java7
 ---> 8fb1905f5b5e
Step 1 : ADD stomp-chat-3.0.0.BUILD-SNAPSHOT.jar /app/
 ---> Using cache
 ---> 5fa52eb71231
Step 2 : EXPOSE 8080
 ---> Using cache
 ---> 940aae24f7bc
Step 3 : ENTRYPOINT /usr/bin/java -jar /app/stomp-chat-3.0.0.BUILD-SNAPSHOT.jar
 ---> Using cache
 ---> b05640830c5b
Successfully built b05640830c5b

The -t switch tags the image with a name used later to reference the image.

Verify the image exists

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docker images
REPOSITORY            TAG                 IMAGE ID            CREATED             VIRTUAL SIZE
mfrasier/stomp-chat   latest              b05640830c5b        23 hours ago        754.2 MB

create and a run docker container from the image

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docker run -p 8080:8080 -d --name chat1 mfrasier/stomp-chat
882ee0e51db9c809906e2f577a56714413bb4daa0d6213ecaa3ba51b23d8ebc8

The run command returns the container id. We should now have a running container which has mapped it’s port 8080 to the vm port 8080 (that’s what the -p switch does). The -d switch tells the container to run detached. The –name switch gives the container a name we can use to reference it, besides the id.

We can verify the container is running with the docker ps command.

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docker ps
CONTAINER ID        IMAGE                        COMMAND                CREATED             STATUS              PORTS                    NAMES
882ee0e51db9        mfrasier/stomp-chat:latest   "/usr/bin/java -jar    22 hours ago        Up About a minute   0.0.0.0:8080->8080/tcp   chat1

test app running in container

on my host the docker vm is at IP address 192.168.59.103 so I point my browser to http://192.168.59.103:8080 to test the app. Be sure to login from multiple browser pages as different people to get the full effect!