{"id":942,"date":"2019-10-04T12:21:48","date_gmt":"2019-10-04T10:21:48","guid":{"rendered":"http:\/\/blog.zhaw.ch\/splab\/?p=942"},"modified":"2019-10-04T16:46:05","modified_gmt":"2019-10-04T14:46:05","slug":"introducing-the-docker-compose-validator","status":"publish","type":"post","link":"https:\/\/blog.zhaw.ch\/splab\/2019\/10\/04\/introducing-the-docker-compose-validator\/","title":{"rendered":"Introducing the Docker Compose Validator"},"content":{"rendered":"\n

When cloud application developers are working with docker-compose<\/code> to combine multiple microservices into a single manageable entity, they can make some easy mistakes. To prevent these mistakes, they can rely on internal validation logic, which however does not catch many of the typical issues. Therefore, researchers at the Service Prototyping Lab<\/a> at Zurich University of Applied Sciences wrote a dedicated quality check and assessment tool targeting developers, but also students trying to learn the technology, which has a wider range of checks. The DCValidator tool is available as a web application (see demo instance<\/a>) or command-line interface. This blog post describes how to check that docker-compose files are free of issues.<\/p>\n\n\n\n

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docker-compose validator Web interface<\/figcaption><\/figure>\n\n\n\n\n\n\n\n

One might ask what is the purpose of this tool when there is the built-in docker-compose validator? This validator unfortunately fails to validate many issues. For example, duplicate keys that result from copy & paste actions, which are incredibly common during the creation of the arguably complex YAML compose files<\/a>. The built-in YAML parser of docker-compose by default ignores the duplicate keys. Imagine that you have some services in your compose file and two of them have the same name but they are different services. In this case, you will lose one of your services and this is not good news! Similar duplication issues exist for port allocations.<\/p>\n\n\n\n

Before we start, let us talk about some common mistakes that developers and students make.
1- The most common things are typo mistakes.
2- Duplicate keys and tags that we mentioned before are another kind of mistakes we can make
3- And some mistakes in values of keys.<\/p>\n\n\n\n

Let’s see an example:<\/p>\n\n\n\n

version: '3'\n\nservices:\n  app:\n    build: \n      context: .\n      args:\n        - IMAGE_VERSION=3.7.0-alpine3.8\n    image: takacsmark\/flask-redis:1.0\n    env_file: .env.txt\n    ports:\n      - 80:5000\n      - 80:5000\n    dns: 888.888.8888\n    networks:\n      - mynet\n  app2:\n    image: ubuntu:latest\n    command: [\"tail\", \"-f\", \"\/dev\/null\"]\n  redis:\n    imge: redis:4.0.11-alpine\n    networks:\n      - mynet\n    volume:\n      - mydata:\/data\n\nnetwork:\n  mynet:\nvolumes:\n  mydata:<\/code><\/pre>\n\n\n\n
In this case, we have duplicate ports, typo mistake, and bad DNS. These issues can be found out with the Docker Compose Validator<\/a>, as explained by the video below.<\/p>\n\n\n
Validating and Quality-Checking Docker Compose Files<\/div><\/div>
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