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Lab II

This lab is desigend to excercise a composed microservice. We will use docker-compose to deliver an application spanning multiple containers.

Create File

Create a file named docker-compose.yml in the top level folder.

Your directory tree should look something like:

labs
│   lab1.md
│   lab2.txt
│   docker-compose.yml
|
└___monolith-app
│   │   ...
│
|___...

You may use any text editor to manipulate this file. In YAML, spaces are extremely important, so make sure to indent lines using spaces only, 2 spaces per indentation level.

Add a the version and services keys into the compose file:

version: "3.7"

services:

Define Services

Our monolithic application is composed of 2 services: The web application, and a database. We'll start with defining the database service.

Add a service key legacy-db under the services list. Don't forget to indent properly!

To the legacy-db service, add:

  • An image specifying "mongodb" version 4.0
  • A ports key containing a list of ports. In the port mapping, state that port 27017 on the host is mapped to port 27017 in the container.

Double check to make sure your indentation is correct.

Add a service key legacy-web to the services list.

To the legacy-web service, add:

  • An image entry, with the value YOURNAME/demo-monolith:latest
  • A build key, with the value of the directory name ./monolith-app
  • Port mapping that maps host port 3000 to the container port 3000.
  • depends_on key, containing a list of dependencies. This container depends on our database container, so use the db container name legacy-db. In YAML, a list can be specified as an array or as an indented line starting with a dash space "- ".
  • An environment entry containing a list of values. We will only add one value: the db connection string. Since your database service is "legacy-db", assign the varibale MONGO_URL1 to the value mongodb://legacy-db:27017/appDemo1.

Running the composed services

The beauty of describing services in this way, is that we can then automate running them with ease.

docker-compose can use this file and run our whole applcation in one command

Ensure any previous lab containers are stopped and removed!

Run the composition using docker-compose

# cd BASE_DIRECTORY
docker-compose up

If all is well, our legacy application should now be running. Point a browser to http://localhost:3000/ and ensure the page renders properly.

No explicit linking is necessary because the 2 containers are created in the same network and the web applicaiton knows the database host name advertised at time of container creation and runtime.

Stop the composed orchestration

Hit CTRL+C to stop the composition.

You may run docker-compose with the -d flag which will daemonize it. In that case, you can stop the composition by running docker-compose down.