container.training/slides/shared/sampleapp.md

Our sample application

• We will clone the GitHub repository onto our node1

• The repository also contains scripts and tools that we will use through the workshop

.exercise[

• Clone the repository on node1:

  git clone https://@@GITREPO@@
  

]

(You can also fork the repository on GitHub and clone your fork if you prefer that.)

---

Downloading and running the application

Let's start this before we look around, as downloading will take a little time...

.exercise[

• Go to the dockercoins directory, in the cloned repo:

  cd ~/container.training/dockercoins
  

• Use Compose to build and run all containers:

  docker-compose up
  

]

Compose tells Docker to build all container images (pulling the corresponding base images), then starts all containers, and displays aggregated logs.

---

More detail on our sample application

• Visit the GitHub repository with all the materials of this workshop:
  https://@@GITREPO@@

• The application is in the dockercoins subdirectory

• Let's look at the general layout of the source code:

  there is a Compose file docker-compose.yml ...

  ... and 4 other services, each in its own directory:

  • rng = web service generating random bytes
  • hasher = web service computing hash of POSTed data
  • worker = background process using rng and hasher
  • webui = web interface to watch progress

---

What's this application?

--

• It is a DockerCoin miner! .emoji[💰🐳📦🚢]

--

• No, you can't buy coffee with DockerCoins

--

• How DockerCoins works:

  • worker asks to rng to generate a few random bytes

  • worker feeds these bytes into hasher

  • and repeat forever!

  • every second, worker updates redis to indicate how many loops were done

  • webui queries redis, and computes and exposes "hashing speed" in your browser

---

class: pic

---

Our application at work

• On the left-hand side, the "rainbow strip" shows the container names

• On the right-hand side, we see the output of our containers

• We can see the worker service making requests to rng and hasher

• For rng and hasher, we see HTTP access logs

---

Connecting to the web UI

• "Logs are exciting and fun!" (No-one, ever)

• The webui container exposes a web dashboard; let's view it

.exercise[

• With a web browser, connect to node1 on port 8000

• Remember: the nodeX aliases are valid only on the nodes themselves

• In your browser, you need to enter the IP address of your node

]

A drawing area should show up, and after a few seconds, a blue graph will appear.

---

class: self-paced, extra-details

If the graph doesn't load

If you just see a Page not found error, it might be because your Docker Engine is running on a different machine. This can be the case if:

• you are using the Docker Toolbox

• you are using a VM (local or remote) created with Docker Machine

• you are controlling a remote Docker Engine

When you run DockerCoins in development mode, the web UI static files are mapped to the container using a volume. Alas, volumes can only work on a local environment, or when using Docker4Mac or Docker4Windows.

How to fix this?

Stop the app with ^C, edit dockercoins.yml, comment out the volumes section, and try again.

---

Stopping the application

• If we interrupt Compose (with ^C), it will politely ask the Docker Engine to stop the app

• The Docker Engine will send a TERM signal to the containers

• If the containers do not exit in a timely manner, the Engine sends a KILL signal

.exercise[

• Stop the application by hitting ^C

]

--

Some containers exit immediately, others take longer.

The containers that do not handle SIGTERM end up being killed after a 10s timeout. If we are very impatient, we can hit ^C a second time!