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Cadavres Exquis "Swarm edition"

Warm-up

If you plan on attending this workshop, you need:

  • A laptop + power cord
  • Install Docker 1.12:
  • Test that your docker installation works fine:
    • docker version should show version 1.12 on both Client and Server side.
    • Run docker run hello-world and check you see the welcome message.
  • Get the source of the lab by git clone [email protected]:CodeStory/lab-docker.git
  • During the workshop, we'll distribute USB keys with the docker images we need for the lab:
    • cd lab-docker
    • docker load -i images.tar will load all the images you need.
  • As an alternate solution, you can load the images directly from the hub:
    • docker pull dockerdemos/lab-web
    • docker pull dockerdemos/lab-words-dispatcher
    • docker pull dockerdemos/lab-words-java
    • docker pull mongo-express:0.31.0
    • docker pull mongo:3.3.15

1 - Look Ma', micro-services on my laptop

Our first version of the application is composed of four micro-services:

  • A web service that uses nginx running on port 80 to serve an HTML5/Js application written in angularJs.
  • A words-java service that runs a java web server on a random port. This server connects to the database and exposes a Rest Api to the web.
  • A db service that runs a mongoDb database on a random port.
  • A db-ui service that runs a web UI on port 8081 to edit the content of the database

Let's run the application

  1. Point Docker CLI to the Docker daemon:

  • If you have Docker for Mac or Docker for Windows, there's nothing to be done. Run docker info to check that everything is up and running.

  • If you have Docker Toolbox, either open the Quick Start terminal or run docker-machine env to show the command you have to run to point to the Docker daemon running on the VirtualBox VM. On OSX, it's typically:

    eval $(docker-machine env default)
  1. Configure Docker Compose to use the first configuration file:
cd lab-docker
cp docker-compose-v1.yml docker-compose.yml
  1. Build and start the application:
docker-compose up -d
  1. Take a look at the logs, to see if there's any error:
docker-compose logs
  1. List the running containers:
docker-compose ps

  Name                       Command               State              Ports
---------------------------------------------------------------------------------------------
labdocker_db-ui_1        tini -- node app                 Up      0.0.0.0:8081->8081/tcp
labdocker_db_1           /entrypoint.sh mongod            Up      27017/tcp
labdocker_web_1          nginx -g daemon off;             Up      443/tcp, 0.0.0.0:80->80/tcp
labdocker_words-java_1   java -DPROD_MODE=true -Xmx ...   Up      8080/tcp

Let's use the application

With Docker for Mac and Docker for Windows, you can open a browser on "http://localhost". With Docker Toolbox, get the ip address of the VM with docker-machine ip default and open a browser on "http://[THE_IP]".

You should see a random composed of 5 random words: a noun, an adjective, a verb, a noun and an adjective. That's a "Cadavre Exquis"! You did it!

However, you'll notice that it's always the same sentence that's displayed. We have to fix that! And will do it without touching the code...

How does it work?

The angularJs application served by the nginx based web service sends 5 http GET queries to the nginx that proxies the words REST service.

That was easy because with docker, each service can be reached on the network via it's name.

On each query, the words service loads all the words from the mongo database, chooses a random one and memoizes it so that future queries are served from the memory and not from the database.

What to explore in this step

  1. The db-ui web UI can be used to configure the list of words in the database.
  • Use this command to find the url for the UI: docker-compose port db-ui 8081
  • Add some nouns, adjectives and verbs, use non-plural and male noun and adjectives, or the grammar will not be correct.
  • Careful, all words added to the database at this stage will be lost for the next stages.
  1. You can improve the web UI:
  • Change something in web/static/index.html
  • Then docker-compose stop web; docker-compose rm -f web; docker-compose build web; docker up -d web, see how this updates a single micro service.
  1. Things to check in this step:
  • Notice the db connexion string in words-java/src/main/java/Main.java
  • Notice the nginx configuration in web/default.conf on location /words/ and check the corresponding code in web/static/app.js
  • Notice in the docker-compose-v1.yml file some services have build and image instructions while others have only image
  • Notice the ports vs expose instructions, try to find a way to call the /verb instruction on the words-java, without changing the yml file.

2 - Run the application with a dispatcher

We are going to change the micro-service based architecture of our application without changing its code. That's neat!

Our idea is to introduce an additional micro-service between the web and the java rest api. This new component is a Go based web server that will later help dispatch word queries to multiple java REST backends.

Let's use the application

  1. Stop the application currently running:
cd lab-docker
docker-compose stop
docker-compose rm -f
  1. Configure Docker Compose to use the second configuration file:
cp docker-compose-v2.yml docker-compose.yml
  1. Build and start the application:
docker-compose up -d
docker-compose logs

As a user, you should see no difference compared to the original application. That's the whole point!

How is that possible?

The web's expectation is that a words host exists on the network and that it responds on port 8080. What we did it renamed the words service to words-java and introduced a new go based service under the name of words.

Step 1, we had: web:80 -> words:8080 (java) Now, we have: web:80 -> words:8080 (go) -> words-java:8080 (java)

Thanks to Docker networking and the expose configuration, we can have two services running on port 8080 without a conflict. An automatic translation will be done by the network. We don't have to change our code. How cool is that?

What to explore in this step

  1. Check the logs and see the dispatcher in action
  • Run docker-compose logs -f and refresh your page at will, check the dispatcher work described in the logs.
  1. Check the dispatcher code
  • Especially the forward function in the words-dispatcher/dispatcher.go source.
  • careful this code is not really efficient but it serves well the purpose of this workshop

3 - Run the application on a shared Swarm with Docker 1.12 services

We are going to the Cloud! Your containers will be send to a shared Swarm composed of multiple nodes. We have already setup the Swarm for you before the talk. You just need to point your Docker CLI to the Swarm rather than to your local Docker daemon. This is done through environment variables. And because our Swarm has TLS enabled, you need a copy of our certificates. We'll pass along a couple of USB keys with the certificates on them. Then follow the instructions below:

  1. Stop the application currently running:
cd lab-docker
docker-compose stop
docker-compose rm -f

  1. Copy the provided certificates from the USB key.

  2. Point your docker client to the proper machine:

If you are on the Google Cloud Swarm cluster:

export DOCKER_TLS_VERIFY="1"
export DOCKER_HOST="tcp://104.155.53.144:2376"
export DOCKER_CERT_PATH="$(pwd)/certificates"

  1. Confirm that docker node ls shows multiple nodes.

  2. Configure Docker Compose to use the third configuration file:

cd lab-docker
cp docker-compose-v3.yml docker-compose.yml
  1. Create a bundle file:
docker-compose bundle -o MY-UNIQUE-TEAM-NAME.dab
docker deploy MY-UNIQUE-TEAM-NAME
docker service ls
  1. Get the port of the web service.
docker service inspect --pretty MY-UNIQUE-TEAM-NAME_web | tail -n1
  1. Open the browser on http://104.155.53.144:PORT

The same application that ran on you machine now runs in the Cloud on a shared Swarm.

How is that possible?

If you compare docker-compose-v2.yml and docker-compose-v3.yml you'll see that all the services now use a private network now. This network is created by Docker Compose. Its name is private, prefixed by the name of your project (ie your team name). It's a network available to your containers only.

Thanks to this private network, multiple similar applications can coexist on a Swarm.

All the services with the same name or alias on a shared network will be reachable on the same DNS name. A client can get all the IPs for the DNS name and start load balancing between the nodes. Nothing complicated to setup!

That's exactly what the words-dispatcher does. To bypass the DNS cache, it searches for all the IPs for the works-java services and uses a random one each time. This effectively load balances queries among all the teams.

What to explore in this step

  1. You can increase the numbers of words-java nodes and see how the dispatcher react.
  • Add more words-java node with docker service scale MY-UNIQUE-TEAM-NAME_words-java=4.
  • You have now 4 words-java containers. Check their numbers with docker service ls
  1. You can kill containers and see them respawned

Docker Features demonstrated

  • Multi-host Networking - Docker 1.9
  • New compose file - Docker 1.10
  • Use links in networks - Docker 1.10
  • Network-wide container aliases - Docker 1.10
  • DNS discovery - Docker 1.11
  • Build in docker-compose up - Docker-Compose 1.7
  • Bundles and Services - Docker 1.12

About 'Cadavres Exquis'

Cadavres Exquis is a French word game, you'll find more on wikipedia page (in French)

How did we create the Swarm?

The Swarm has been created on Google Cloud with the init_swarm_google.sh script. Take a look to what we do there but you'll need an account and this may cost you money. You can also try it on your own laptop by running the init_swarm_vbox.sh, you'll need virtualbox and docker-machine