Page 5 - Docker

Before Docker officially supported named volumes, the community solved the problem of persistent data with a workaround: a dedicated, never running container that only declared data directories and passed them on to other containers via --volumes-from. This data-only container pattern was standard for years, but is now replaced by named volumes in the vast majority of cases, with only a few remaining niches where the old approach still plays a role.

Without a systematic Docker cleanup strategy, CI runners and production servers fill up within weeks with unused images, orphaned volumes, and stale build caches. The right automation concept prevents disk exhaustion without accidentally deleting important data.

An uncontrolled flood of latest tags and anonymous Docker Hub pulls puts every production environment at risk. Teams that run a private Docker registry, adopt meaningful image versions, and define retention policies create traceable, reproducible builds and significantly reduce the risk of outages.

Before a service runs in production with multiple replicas in Kubernetes or Docker Swarm, it is worth testing locally with deploy.replicas in Docker Compose. This way, port conflicts, shared volumes and load balancing behavior can be uncovered on the development machine, instead of noticing them only after a production rollout.

A Varnish, Redis and OpenSearch sidecar with default configuration runs, but rarely delivers the performance a Magento shop needs under real load. This article shows how these three sidecars are deliberately fine-tuned as containers, from VCL rules through eviction policies to JVM heap sizing, instead of relying on factory defaults.

Anyone maintaining three separate compose files for dev, test and CI ends up writing configuration three times and regularly forgets to sync changes across them. Docker Compose Profiles solve this problem at the root: services are only started when the matching profile is active, one file for every environment.

The choice of minimal base image determines compatibility, debugging capability and maintenance effort for the entire lifetime of a Docker image. Alpine with musl libc, Debian slim with the full glibc ecosystem, distroless without any shell, and scratch as a completely empty foundation solve different problems and each fit different project requirements.

Docker is not just a runtime, it is a portable build environment. Teams that create deployment artifacts from Docker builds get reproducible binaries, static assets and archives without installing the build toolchain on the CI server or the developer machine.

Docker Compose can do more than launch main services. Sidecar containers forward logs and export metrics. Utility containers provide CLI tools without a local install. Init containers run before the main service and carry out database migrations. One off jobs handle maintenance tasks on demand. This article explains all four patterns, each with the right tool for the right purpose.

Port conflicts between projects, missing HTTPS in development, and confusing hostnames are classic pain points in team Docker networking. With Traefik as a central reverse proxy, mkcert for local HTTPS certificates, and cleanly isolated Docker networks, these problems can be solved once and for all.