Docker to Kubernetes: Migration Path

Many organisations start their container journey with Docker Compose — it is simple, familiar, and works well for small-scale deployments. But as applications grow in complexity and traffic, the limitations of Docker Compose become apparent: no built-in service discovery, limited scaling capabilities, no rolling updates, and no self-healing. Kubernetes addresses all of these, but the migration path requires careful planning.

When to Move from Docker to Kubernetes

Not every application needs Kubernetes. Before migrating, consider whether your use case justifies the added complexity:

• You need horizontal scaling — your services need to scale up and down based on traffic, and manual scaling with Docker Compose is no longer practical.
• You need high availability — you want automatic failover, health checks, and self-healing without manual intervention.
• You run multiple services — your application consists of many microservices that need service discovery, load balancing, and inter-service communication.
• You need rolling updates — deploying new versions without downtime is a requirement, and Docker Compose does not support this natively.
• You operate across multiple environments — you need consistent deployments across development, staging, and production with environment-specific configuration.

Preparing Your Docker Images

Before migrating to Kubernetes, ensure your Docker images follow best practices:

• Use specific image tags — avoid the "latest" tag. Pin to specific version tags or SHA digests for reproducible deployments.
• Externalise configuration — move all environment-specific configuration out of the image and into environment variables. Kubernetes ConfigMaps and Secrets will replace your .env files.
• Implement health checks — add HTTP or TCP health check endpoints to your applications. Kubernetes liveness and readiness probes depend on these.
• Handle graceful shutdown — ensure your application responds correctly to SIGTERM signals, completing in-flight requests before exiting. Kubernetes sends SIGTERM before killing pods.
• Log to stdout/stderr — Kubernetes expects applications to write logs to standard output. Avoid writing to log files inside the container.

Translating Docker Compose to Kubernetes Manifests

Each Docker Compose service translates to a set of Kubernetes resources:

• Service definition becomes a Deployment (for stateless services) or StatefulSet (for databases and other stateful workloads).
• Port mappings become Kubernetes Services (ClusterIP for internal, LoadBalancer or Ingress for external access).
• Volumes become PersistentVolumeClaims backed by cloud storage providers.
• Environment variables become ConfigMaps (for non-sensitive data) and Secrets (for credentials and keys).
• depends_on is handled through readiness probes and init containers rather than explicit dependency declarations.

Tools like Kompose can automatically convert Docker Compose files to Kubernetes manifests, but the output typically needs significant refinement. It is better to understand the mapping and write clean manifests from scratch.

Choosing Your Kubernetes Platform

You have several options for running Kubernetes:

• Managed Kubernetes — EKS (AWS), AKS (Azure), or GKE (Google Cloud) handle the control plane for you. This is the recommended approach for most organisations. See our managed vs self-managed comparison.
• Self-managed — running Kubernetes on your own infrastructure with tools like kubeadm or k3s. This gives maximum control but requires significant operational expertise.
• Local development — use minikube, kind, or Docker Desktop's Kubernetes for local development and testing before deploying to production clusters.

Migration Strategy: Phased Approach

Avoid a big-bang migration. Instead, move services incrementally:

1. Start with stateless services — web applications, APIs, and worker processes are the easiest to migrate because they do not require persistent storage management.
2. Set up CI/CD for Kubernetes — build a GitOps-based delivery pipeline that builds images and deploys to your cluster automatically.
3. Migrate supporting services — move message queues, caches, and other infrastructure components. Consider using managed services (e.g., ElastiCache, Azure Cache for Redis) instead of self-hosting.
4. Handle databases carefully — databases are the trickiest to migrate. Evaluate whether managed database services are a better option than running databases in Kubernetes.
5. Decommission Docker Compose — once all services are running on Kubernetes and validated, retire the Docker Compose setup.

How ICTLAB Can Help

ICTLAB guides Belgian organisations through the migration from Docker to Kubernetes as part of our DevOps and cloud services. We assess your current container workloads, design the target Kubernetes architecture, and execute the migration in phases — ensuring zero downtime and building your team's skills along the way.