Docker and Container Deployment

When containerisation fits best

Containerisation fits best when the application behaves differently on different machines or servers, or when the deployment process involves installing dependencies directly on the host operating system. Common triggers include a developer saying it works on my machine, a server migration that requires reinstalling every dependency manually, or a stack where multiple services need isolated environments. Docker Compose is particularly useful when the application depends on supporting services like MongoDB, Redis, or PostgreSQL and the team wants a single command to start the entire stack. It is also valuable when the team wants to standardise the development environment so every developer runs the same setup without manual configuration.

What a typical container engagement looks like

The engagement starts by reviewing the application runtime: what language, what dependencies, what supporting services, and what file system access is needed. We write or refine a Dockerfile that produces a production-appropriate image, using multi-stage builds where applicable to keep the final image small. Docker Compose is configured to orchestrate the application container alongside any database, cache, or proxy services, with named volumes for persistent data and a defined network for inter-service communication. After the compose file is ready, we test the full stack, verify that volumes persist data across container restarts, check log output is accessible, and validate health checks. The engagement closes with documentation on how to build, run, update, and troubleshoot the containerised stack.

• Runtime review and Dockerfile authoring or refinement
• Docker Compose orchestration with volumes and networking
• Full-stack testing including persistence and health checks
• Documentation for build, run, update, and troubleshooting

Common pitfalls and how they are avoided

The most common Docker pitfall is running as root inside the container, which creates security issues and file permission problems on bind mounts. We add a non-root user to the Dockerfile and configure the application to run with appropriate permissions. Another frequent issue is large images caused by including development dependencies, build tools, or unnecessary system packages in the final image. Multi-stage builds separate the build stage from the runtime stage, reducing image size significantly. Containers that do not persist data properly are also common, where database or upload data disappears after a container restart because volumes were not configured. We define named volumes for every directory that must persist and document backup procedures for those volumes.

Security and access considerations

Container security begins with the Dockerfile. We avoid running the container as root, do not hardcode secrets in the image, and do not store credentials in environment variables visible through docker inspect. Secrets are passed through Docker Compose environment files or mounted as files from the host, depending on the deployment model. We review the Docker host's security, ensuring the Docker socket is not exposed to the application or the network, and that the user who can run Docker commands is appropriately restricted. Network configuration is reviewed to ensure containers only expose the ports necessary for their function, and that database containers are not accessible from the public network.

Operational handover and runbooks

Container handover means the team can build images, start and stop the stack, view logs, and troubleshoot containers without external help. The runbook covers the docker-compose commands for starting, stopping, rebuilding, and viewing logs. It documents how to check container health, how to enter a running container for debugging, and how to inspect volumes to verify data persistence. Common failure scenarios and their resolution steps are included, such as a container that exits immediately due to a configuration error, a volume permission issue, or a port conflict. The team should understand how to update a container image and redeploy without downtime when the application supports it.

Monitoring, validation, and rollback

After the container stack is running, we validate every component. The application container should respond to health checks, database containers should accept connections, and the network should allow inter-service communication while blocking external access to internal services. We verify that restarting a container preserves its data through named volumes and that the docker-compose restart policy brings containers back after a host reboot. Rollback is handled by keeping the previous image tag available and documenting how to pin the compose file to a specific image version. If a new deployment introduces a regression, the team can revert the image tag and restart the stack to return to the previous state.

Collaboration with your in-house team

Container work requires understanding the team's development environment, deployment infrastructure, and existing practices. We review how the team currently runs the application locally and whether Docker is already part of their workflow. If the team is new to containers, we walk through the core concepts and ensure they can build, run, and troubleshoot independently. If the team already uses Docker, we focus on production readiness, image optimisation, and compose orchestration improvements. We also discuss how containers interact with the team's CI/CD pipeline, ensuring images are built and pushed through an automated process rather than built manually on the production server.

What good looks like after containerisation

A well-containerised application starts with a single docker-compose up command and produces a fully running stack with the application, database, and any supporting services. The Dockerfile produces a minimal image with only runtime dependencies. Volumes persist data across container restarts. Health checks detect and report container failures. Logs are accessible through docker-compose logs without requiring SSH into the container. The team can rebuild and redeploy the stack by running documented commands. The previous image version is tagged and available for rollback. If a new developer can run the full stack locally after reading the documentation, the containerisation has achieved its goal of environment consistency.