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Docker & Kubernetes · Question Set
Docker Compose & Swarm Mode interview questions for placements and exams.
Questions
11
Included in this set
Subject
Docker & Kubernetes
Explore more sets
Difficulty
Mixed
Level of this set
Go through each question and its explanation. Use this set as a focused practice pack for Docker & Kubernetes.
In docker-compose.yml you use `depends_on:` to make one service wait until the other has been started. It does *not* guarantee the dependent service is fully ready — only that it has been started.
services:
web:
depends_on:
- dbFor complete preparation, combine this set with full subject-wise practice for Docker & Kubernetes. You can also explore other subjects and sets from the links below.
A Dockerfile gives instructions for building an image (base, copy, run, cmd). A Compose file describes services (built from images or specified via Dockerfile), networks, volumes and how they relate at runtime. They serve different roles in container workflows.
Docker Compose allows you to define services, networks and volumes for a multi-container application in a compose YAML file, then bring them up with a single command. It simplifies orchestration for local development and small deployments.
Docker Swarm is Docker’s built-in orchestration system. It allows you to run services across multiple nodes, manage desired state, replicate containers, and provide basic scheduling and load balancing.
The `docker swarm init` command turns a Docker host into a manager node of a swarm. After that other nodes may join as manager or worker. It sets up the Raft store, leadership election and enables swarm mode.
docker swarm init --advertise-addr 192.168.0.10
In Docker Swarm, a manager node handles control plane tasks: scheduling services, maintaining cluster state (via Raft consensus), handling API requests. A worker node executes tasks: runs container instances of services as assigned by managers. Managers can also run tasks unless configured otherwise. Clear role understanding is essential for designing scalable clusters.
`docker stack deploy` is used in Swarm mode and interprets a compose file to deploy services across the swarm nodes with built-in load balancing (routing mesh). `docker-compose up` works on a single Docker host and sets up containers without swarm scheduling or replication.
You scale a service in Swarm using `docker service update --replicas <N> <service_name>` or at creation `--replicas <N>`. Best practices include: distributing replicas across nodes (avoid single host bottleneck), define resource limits (CPU/memory) to prevent noisy neighbours, monitor cluster state and service health, use update/rollback policies to minimise downtime and ensure version consistency, and use overlay networks for efficient inter-service communication. Preparing for scaling issues shows readiness for real-world deployments.
Compose profiles let you tag services with `profiles: ["dev"]` or `profiles: ["prod"]`. When running `docker compose --profile prod up` only services tagged for prod plus default run. This helps reuse the same compose file for multiple environments. Refer to official docs.
In Swarm mode, services are the basic deployment unit. `docker service create --name web --image nginx --replicas 3` instructs the swarm to run three tasks of nginx, distribute them across available nodes, and manage their state.
In Swarm mode a rolling update means you update a service image and Swarm replaces tasks one by one (or per update-config) while keeping old ones running, maintaining service availability. Command: `docker service update --image new:tag <service>`. A blue-green deployment instead runs a parallel version (green) alongside current (blue), then switches traffic over, then removes the old version. Rolling updates are simpler for small services; blue-green gives strong isolation and quick rollback. Knowing both shows maturity in deployment strategy.