Docker exercises

Exercise: containerising a Node.js webserver

• Create a simple Node.js web server
  • Create index.js to expose a web server on port 3030

      // content of index.js
      const http = require('http');
      const port = 3030;
      const requestHandler = (request, response) => {
      console.log(request.url);
      response.end('Hello Node.js Server!');
      };
      const server = http.createServer(requestHandler);
      server.listen(port, (err) => {
      if (err) { return console.log('something bad happened', err); }
      console.log(`server is listening on ${port}`);
      });
    

  • Test locally
    • Install package.json using npm install
    • Start using npm start
    • curl localhost:3030 or open in local browser
    • Terminate local service after testing
• Write a Dockerfile to:
  • Use a Node.js base image
  • Copy package.json over to image and npm install at build time
  • Run npm start at container start time
  • EXPOSE port 3030 from the container
• Instantiate this image and connect to your container
  • Verify that you can connect to the web service from within the container
  • Use docker container ls to show exposed ports for running containers
  • Verify that you can connect to the web service from outside the container
    • e.g. on host machine
  • Capture all your commands in scripts (good IAC practice)
• Run your container as a non-root user, e.g. user 1000
  • Modify your container to run all processes as user 1000
  • Set appropriate file permissions to enable access to your non-root user

The solution to the ‘containerising’ exercise is available as part of our open-source Devops-Workstream.

Exercise: augment existing Dockerfile

• Create a Dockerfile that augments the existing NGINX Dockerfile
  • Use the FROM keyword to reference the latest nginx
• Install an additional package such as procps (for ps commands)
  • using the package manager built into your chosen distribution
• Copy a local nginx.conf file into your container
  • You might base your configuration on a simplified version of this Nginx Example Configuration
    • Alternatively see solution for sample config
• Copy a local website into your container
  • A single index.html file will suffice, but you can enrich it if you’d like
• Run NGINX as a non-root user, e.g. user 1000
  • Hint: you’ll need to direct NGINX to use /tmp subfolder for all writable outputs

The solution to the ‘augment’ exercise is available as part of our open-source Devops-Workstream.

Exercise: environment variables

• Build on the ‘containerising’ exercise to pass in a PORT environment variable
  • Extend the Node.js code to look for the PORT environment variable
    • Add to package.json

        ...
        "main": "src/index.js",
        "dependencies": {
        "dotenv": "^8.2.0",
        "nodemon": "^2.0.1"
        },
        ...
      

  • Modify the index.js to accept an environment variable, but fall back to a default if absent

      ...
      const http = require('http');
      const env = require('process').env;
      require('dotenv').config();
      const port = env.PORT || 8080;
      ...
    

• Initially don’t set a environment value for port
  • Test to see if it’s exposed on 8080, both in the container and to the host
• Set a value for the environment variable in Dockerfile
  • Connect into the machine and echo $PORT to see environment value
  • Retest access on 8080 and your new value, both in the container and to the host
    • Hint: use docker container ls to see what your container exposes by default
• Set a value for PORT in the docker run command that you use to instantiate your container
  • Retest access again

The solution to the ‘environment variables’ exercise is available as part of our open-source Devops-Workstream.

Exercise: volumes

• Build on the ‘augment’ exercise to share volumes into your container
  • Instead of using COPY to make a duplicate of your nginx.conf
    • mount the file as a volume
• Try modifying your config then restarting your container
  • Hint: you can use docker logs <container_name> to see start-up logs from NGINX
• Repeat this process for the local website you made previously
  • Instead of using COPY to make a duplicate of your local website
    • mount the directory as a volume
• Modify your local website and restart your container

The solution to the ‘volumes’ exercise is available as part of our open-source Devops-Workstream.

Exercise: docker-compose

• Write a docker-compose.yml file to bring up an ELK stack, using container images:
  • Elasticsearch docker.elastic.co/elasticsearch/elasticsearch:7.10.0
  • Logstash docker.elastic.co/logstash/logstash:7.10.0
  • Kibana docker.elastic.co/kibana/kibana:7.10.0
• Bring your stack up using docker-compose up
  • You might choose to run that in a separate process (using &) to avoid blocking your command prompt
• Pass an environment variable to Elasticsearch:
  • discovery.type=single-node
• Expose port 9200 for Elasticsearch and 5601 for Kibana
  • Test internal (in-container) and external (on-guest) access to both services
• Ensure that Elasticsearch spins-up before Logstash and Kibana using the depends_on relationship

The solution to the ‘docker-compose’ exercise is available as part of our open-source Devops-Workstream.

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