Step-by-step articles on Containers, part of our Cloud & DevOps collection.
Showing 20 articles
Docker packages an application with everything it needs (runtime, libraries, config) into an image . Running an image creates a container : an isolated process that behaves the same on your laptop, a CI runner and a production server. Images vs containers An i...
Kubernetes runs containers across a cluster of machines and keeps them in the state you describe. You don't say "start three containers"; you declare "there should always be three", and Kubernetes makes it so, even when machines fail. Pod The smallest unit: on...
A Dockerfile that "works" and one that's good for production differ in image size, build speed, security and how the app shuts down. Here's a solid template. # syntax=docker/dockerfile:1 # ---------- dependencies (all, for building) ---------- FROM node:22-alp...
This walkthrough takes a container image all the way to a running, scalable app on a local Kubernetes cluster. 1. Create a local cluster # kind = Kubernetes in Docker brew install kind kubectl # or see each project's install docs kind create cluster --name dev...
Docker Compose describes a multi-container setup in one file. One command starts your API, database, cache and anything else the project needs, the same way on every developer's machine. compose.yaml services: api: build: . ports: - "3000:3000" environment: DA...
The same image should run in development, staging and production. What changes between them (URLs, feature flags, credentials) belongs in ConfigMaps and Secrets. ConfigMap for non-sensitive settings apiVersion: v1 kind: ConfigMap metadata: name: api-config dat...
Smaller images pull faster, start faster, cost less to store and contain fewer packages with vulnerabilities. Going from 1.2 GB to under 200 MB is common. 1. Choose a smaller base image node:22 (Debian full) - large, has build tools. node:22-slim - Debian with...
Probes tell Kubernetes about the health of each container. Configured well, they give you zero-downtime deploys and self-healing. Configured badly, they can restart healthy Pods in a loop and turn a small issue into an outage. The three probes Readiness - "can...
Most "it can't connect" problems with Docker come from a few networking rules. Once you know them, they're easy to reason about. User-defined bridge networks docker network create appnet docker run -d --name db --network appnet -e POSTGRES_PASSWORD=secret post...
Requests and limits tell Kubernetes how much CPU and memory a container needs and may use. They affect scheduling, performance and stability, and getting them wrong is a top cause of mysterious slowdowns and crashes. resources: requests: cpu: 250m # 0.25 of a...
Slow Docker builds usually re-download dependencies that haven't changed. BuildKit, the default builder in modern Docker, has features designed to stop that. 1. Order layers from least to most frequently changed COPY package.json package-lock.json ./ # changes...
Traffic changes through the day. The Horizontal Pod Autoscaler (HPA) adds Pods when load rises and removes them when it falls, so you pay for what you use and stay fast at peak. Prerequisites metrics-server installed in the cluster (most managed clusters inclu...
Containers isolate processes, but a careless image or run command can undo most of that protection. These practices close the common gaps. 1. Don't run as root RUN addgroup -S app && adduser -S app -G app USER app If an attacker exploits your app, they get the...
Services are reachable inside the cluster. To route outside HTTP traffic to them by hostname and path, Kubernetes offers two APIs: the long-standing Ingress and its successor, the Gateway API . Ingress apiVersion: networking.k8s.io/v1 kind: Ingress metadata: n...
A running process isn't necessarily a working one. It might be deadlocked, out of database connections or stuck in a crash loop. Health checks and restart policies help Docker notice and react. HEALTHCHECK in a Dockerfile HEALTHCHECK --interval=30s --timeout=3...
Helm is a package manager for Kubernetes. A chart is a bundle of templated manifests; a release is an installed copy of a chart with your settings ( values ). Installing software helm repo add bitnami https://charts.bitnami.com/bitnami helm search repo redis h...
When a container doesn't behave, work from the outside in: what does it log, how did it exit, what does its configuration look like, and what is happening inside? 1. Logs docker logs api # everything written to stdout/stderr docker logs -f --tail 100 api # fol...
When something breaks in Kubernetes, the answer is usually in a handful of commands. Start with the Pod's status, then events, then logs. First look kubectl get pods -n shop -o wide # status, restarts, node kubectl describe pod api-7d9f-x2k -n shop # events at...
Containers are disposable, but data often isn't. Docker offers three ways to give a container storage beyond its own temporary layer. Named volumes docker volume create pgdata docker run -d -v pgdata:/var/lib/postgresql/data postgres:17 docker volume ls docker...
Kubernetes Deployments roll out new versions gradually by default. But "gradual" isn't automatically "zero downtime": dropped connections during shutdown are the usual culprit. These settings close the gaps. 1. Rolling update strategy spec: replicas: 4 strateg...
