Topic
A container packages an application with its dependencies and runs it against the host kernel, which is why it starts far faster than a virtual machine, which has to boot an entire operating system with its own kernel first. That single difference is the reason containers became the default unit of deployment.
Most container problems are not really about Docker. They are about image size, layer caching, what happens to writes inside a container that gets recreated, and how a process behaves when it receives SIGTERM. The material below covers the mechanics first, because the debugging only makes sense once the model is clear.
Existing pages in an order where each step answers a question the previous one raised, with an exercise at the end.
Step-by-step, with copy-paste commands and an assistant that answers questions about the guide you are reading.
Named errors and symptoms, each with its causes, a command that confirms each one, and the fix.
localhost used instead of the other container's name, no shared network, or the app listening only on its own loopback. Each has a one-line check below.no signatures found means nothing is attached, while no matching signatures: none of the expected identities matched is followed by the subject and issuer that actually signed.openssl s_client tells them apart in one command.docker compose build fails when a Dockerfile, a build secret or an SSH key lives outside the project directory. Bake now enforces its filesystem permissions in the mode Compose uses (30 Sep 2026). The fix is merged in Compose but in no release yet. Until it is, move the file inside the build context, or set BUILDX_BAKE_ENTITLEMENTS_FS=0 for that one trusted build.BUILDX_NO_DEFAULT_OCI_ARTIFACT=1 (Buildx 0.36.1 or later), then push again.Pairs of things that get mistaken for one another, and the problem the mix-up causes.
-p is what actually makes a port reachable through your machine's own addresses, such as localhost, and from other machines. Neither one changes what address your application binds to inside the container.The design decision behind the behaviour, and what it costs you.
A failure followed step by step: what each part of the system does, and what you can change.
Run in your browser; nothing you paste is sent anywhere.
A question, then the follow-ups an interviewer asks when the first answer is right.
Ordered by how much they are read.
Kubernetes explained through the control loop under Pods, Deployments and Services, so you can predict what the cluster will do, not just name its parts. Most introductions stop at the nouns.
Neeraj Jha
Updated
Set up a production-grade monitoring stack with Prometheus and Grafana — metrics collection, PromQL queries, alerting, and dashboards.
Neeraj Jha
Updated
How to get oriented in a Kubernetes YAML file you did not write: four hundred lines, in production, by somebody who left. An order that works, and why the file may not be what is running.
Neeraj Jha
Updated
Deep dive into Kubernetes networking — ClusterIP, NodePort, LoadBalancer, Ingress controllers, CoreDNS, and Network Policies explained with examples.
Neeraj Jha
Updated
Most teams generate an SBOM and never read one. The single question it answers well, the four things it does not, and the difference between a compliance artifact and an operational one.
Neeraj Jha
Master Helm charts for Kubernetes — chart structure, values, templates, repositories, environment management, and deployment best practices.
Neeraj Jha
Updated
The same ten-item checklist, ordered by the threat each item actually closes — and honest about which three matter most and what none of them protect you from.
Neeraj Jha
Updated
Why pip install now fails with externally-managed-environment on Ubuntu 24.04, Debian 12 and Homebrew, and the three fixes that work: a venv, pipx, or apt. Plus why it passes in GitHub Actions and fails in docker build.
Neeraj Jha
Since Docker 29.7, docker push can fail with blob unknown to registry on GitLab or with timeout awaiting response headers on slow registries. How to tell which one you have, and what fixes each.
Neeraj Jha
Real questions from the community, with an accepted answer.