How do you migrate legacy applications to containerized environments?

2 Refactor your code

The next step is to refactor your code to make it more compatible with the containerization principles. This may involve breaking down your monolithic applications into smaller and independent microservices, which can communicate through APIs or messaging systems. You may also need to update your code to use the latest technologies, frameworks, and standards, and to remove any unnecessary or redundant components. You should also adopt a DevOps approach, which involves using tools and practices such as version control, continuous integration, continuous delivery, and testing, to automate and streamline your development and deployment processes.

3 Build your images

The third step is to build your container images, which are the executable files that contain your code, dependencies, and configuration. You need to create a Dockerfile, which is a text file that specifies the instructions for building your image. You should follow some best practices for writing your Dockerfile, such as using a base image that matches your application's requirements, minimizing the number of layers and commands, avoiding unnecessary files and data, and using labels and tags to identify your images. You can use tools such as Docker Build or Docker Compose to help you build your images.

4 Test your containers

The fourth step is to test your containers, which are the instances of your images that run on the container engine. You need to verify that your containers function correctly, meet your performance and security expectations, and integrate well with other containers and services. You should use tools and frameworks such as Docker Test, Docker Scan, or Selenium to help you test your containers. You should also use a staging environment, which is a replica of your production environment, to simulate the real-world conditions and scenarios that your containers will face.

5 Deploy your containers

The fifth step is to deploy your containers, which means launching them on the target platform that supports the container engine. You need to choose a platform that meets your scalability, reliability, and availability needs, such as a cloud service, a virtual machine, or a physical server. You also need to use a container orchestration tool, such as Kubernetes or Docker Swarm, to help you manage your containers' lifecycle, distribution, networking, and monitoring. You should follow some best practices for deploying your containers, such as using a blue-green or a canary strategy, which involves gradually rolling out your new containers while keeping your old ones running, to minimize the risk of downtime and errors.

6 Monitor and optimize your containers

The sixth step is to monitor and optimize your containers, which means collecting and analyzing data about your containers' performance, health, and behavior. You need to use tools and metrics such as Docker Stats, Prometheus, or Grafana to help you monitor your containers. You should also use tools and techniques such as Docker Prune, Docker Squash, or Docker Slim to help you optimize your containers' size, speed, and efficiency. You should also be ready to troubleshoot and resolve any issues or anomalies that may arise with your containers, using tools such as Docker Logs, Docker Inspect, or Docker Exec.

7 Here’s what else to consider

This is a space to share examples, stories, or insights that don’t fit into any of the previous sections. What else would you like to add?