tp-docker-12.md

Starting a Compose App

In this exercise, we will learn how to:

• Read a basic docker compose yaml file and understand what components it is declaring
• Start, stop, and inspect the logs of an application defined by a docker compose flag

Preparing Service Images

1. Download the Dockercoins app from github:

$ git clone -b ee2.0 https://github.com/docker-training/orchestration-workshop.git
$ cd orchestration-workshop/dockercoins

This app consists of 5 services: a random number generator rng, a hasher, a backend worker, a redis queue, and a web frontend; the code you just downloaded has the source code for each process and a Dockerfile to containerize each of them.

2. Build each of the images corresponding to the rng, the hasher, worker and webui services:

$ docker image build -t user/dockercoins_hasher:1.0 hasher
$ docker image build -t user/dockercoins_webui:1.0 webui
$ docker image build -t user/dockercoins_worker:1.0 worker
$ docker image build -t user/dockercoins_rng:1.0 rng

Starting the App

1. Stand up the app:

$ docker-compose up

After a moment your app should be running; visit <ip>:8000 to see the web frontend visualizing your rate of Dockercoin mining.

2. Logs from all the runnings services are sent to STDOUT. Let's send this to the background instead; kill the app with CTRL+C, sending a SIGTERM to all running processes; some exit immediately, while others wait for a 10s timeout before being killed by a subsequent SIGKILL. Start the app again in the background:

$ docker-compose up -d

3. Check out which containers are running thanks to Compose:

$ docker-compose ps

4. Compare this to the usual docker container ls; do you notice any differences? If not, start a couple extra containers using docker container run ... and check again.

Viewing Logs

1. See logs from a Composed-managed app via:

$ docker-compose logs

2. The logging API in Compose follows the main Docker API closely. For example, try following the tail of the logs just like you would for regular container logs:

$ docker-compose logs --tails 10 --follow

Note that when following a log, CTRL+S and CTRL+Q pauses and resumes live following; CTRL+C exits follow mode as usual.

In this exercise you saw how to start a pre-defined Compose app, and how to inspect its logs. Application logic was defined in each of the five images we used to create containers for the app, but the manner in which those containers was created was defined in the docker-compose.yml file; every aspect of how many containers we want for each service, what networks to attach thos containers to and what other parameters are desired, is captured in this manifest. Finally, the different elements of Dockercoins communicated with each other via service name; the Docker daemon's internal DNS was able to resolve traffic destined for a service, into the IP or MAC address of the corresponding container.