Prove your Docker skills
Plenty of developers can run a container. Fewer can explain why an image is huge, why a build cache keeps missing, or why a container dies on start. Lemma records that deeper Docker skill.
Preparing for an interview? Docker interview questions, junior to senior
What Docker competence looks like
Someone fluent in Docker writes Dockerfiles that build fast and ship small. They order layers so the cache works, use multi-stage builds to leave compilers behind, and run as a non-root user by default. Secrets stay out of images, and base images are pinned and kept current.
When a container misbehaves, they debug methodically. They read the logs, exec into the container, check the entrypoint and environment, and compare it with what works locally. They use Compose to make local environments match production closely enough that 'works on my machine' stops being a meeting topic.
Live container troubleshooting
60 min · Learning · with Ava T.
Ava T. rated the session
Practitioner · after the call
Clear reasoning on dockerfile design. Talked through trade-offs first.
Dockerfile design
Layer ordering, caching and multi-stage builds that keep images fast to build and small to ship.
Image security
Non-root users, minimal base images, pinned versions and keeping secrets out of layers and history.
Docker Compose
Multi-service local environments with networks, volumes and health checks that mirror production behaviour.
Networking and volumes
How containers reach each other, publish ports and persist data without surprises on restart.
Debugging containers
Reading logs, inspecting state and exec-ing in to find why a container crashes or hangs.
Registries and CI builds
Tagging, pushing and building images in CI so every deploy uses a known, reproducible artifact.
What counts as evidence of Docker skills?
Certificates in Docker show an exam was passed. Lemma records how you work: sessions where you talked through a design or an incident, an adaptive test, and configuration in repositories you link. Every entry says where it came from. See the evidence methodology for how each source is weighed.
Docker
Clara W. · SCI recomputed 9 Oct
Evidence · 4 entries
- Verified
Dockerfiles and Compose in a repo
GitHub connector · 9 Oct
- Level 7.2
Diagnosing a problem Dockerfile
Adaptive assessment · 2 Oct
- Rated 5.0
Live container troubleshooting
Live session · 24 Sep
- Practice
Drills on layers and networking
AI tutor practice · 11 Sep
Dockerfiles and Compose in a repo
Connect GitHub and attach a repository or commit with your Dockerfiles and Compose setup. Lemma confirms your account can access it and re-checks the link over time.
Diagnosing a problem Dockerfile
The adaptive assessment shows realistic situations, such as a Dockerfile that bloats, leaks a secret or fails to start, and you choose the correct diagnosis or fix from the options.
Live container troubleshooting
In a session, a practitioner hands you a misbehaving container setup and watches you diagnose it. Methodical debugging, not memorised commands, is what earns a strong rating.
Drills on layers and networking
The AI tutor gives short exercises on caching, multi-stage builds and container networking. It prepares you for assessments and adds only a small, capped amount to practice.
How is a Docker skills test run on Lemma?
The Docker test is adaptive, 15 to 25 questions on failure modes, permissions and cost rather than service names, and it stops once your level holds steady. With sessions and linked work it sets your Docker SCI, where recent evidence carries more weight.
An image is 1.4 GB and ships the compiler. What reduces it most?
- AA .dockerignore on its own
- BSquash all the layers
- CA multi-stage build with a slim runtime
- DPin the base image tag
Attach your container setups
Connect GitHub and link the repositories where your Dockerfiles and Compose files live. A reviewer can see you have containerised real services, not just followed a tutorial.
Debug a setup in a live session
Book a session with a Docker practitioner and work through a broken or slow container setup together. They rate how you narrow the problem down and explain the fix.
Pass the adaptive Docker assessment
Scenario-based multiple-choice questions cover images, networking and security. Difficulty adjusts after every answer, harder questions count for more, and each one is timed with no going back.
Docker skills: common questions
How do I prove Docker skills to an employer?
What Docker questions come up in DevOps interviews?
What does a good Dockerfile look like in a portfolio?
Should I learn Docker before Kubernetes?
Skills related to Docker
Browse the skills directoryDevOps
Evidence of how you build pipelines, ship safely and keep systems observable.
Evidence for DevOpsAWS
Evidence that you can design, secure and run workloads on AWS, not just name services.
Evidence for AWSCloud architecture
Show how you design cloud systems that scale, fail gracefully and stay affordable.
Evidence for cloud architectureGo
Prove you write clear, concurrent Go services, with evidence from live code and connected repositories.
Evidence for Go
Start your Docker evidence record.
Lemma is in early access. Request an invite and we will email you when your place is ready.