Database containers for local development in Docker - Mini Project: Build & Apply

Database containers for local development

📖 Scenario: You are a developer who wants to run a database locally using Docker. This helps you test your applications without installing the database directly on your computer.

🎯 Goal: You will create a Docker command to run a PostgreSQL database container locally with a set username, password, and database name. Then, you will check if the container is running.

📋 What You'll Learn

Use the official PostgreSQL Docker image version 15

Set environment variables for POSTGRES_USER, POSTGRES_PASSWORD, and POSTGRES_DB

Map the container port 5432 to the host port 5432

Name the container 'local-postgres'

Verify the container is running using a Docker command

💡 Why This Matters

🌍 Real World

Developers often use database containers locally to avoid installing databases directly on their machines. This makes setup faster and keeps the system clean.

💼 Career

Knowing how to run and manage database containers is essential for developers and DevOps engineers to create consistent development environments and simplify testing.

1

Create the Docker run command for PostgreSQL

Write a Docker command to run a PostgreSQL container named local-postgres using the image postgres:15. Set environment variables POSTGRES_USER to devuser, POSTGRES_PASSWORD to devpass, and POSTGRES_DB to devdb. Map the container port 5432 to the host port 5432. Use the docker run command with the -d flag to run in detached mode.

Docker

# Write the docker run command to start the PostgreSQL container
# Your code here

Hint

Use docker run -d --name local-postgres -e POSTGRES_USER=devuser -e POSTGRES_PASSWORD=devpass -e POSTGRES_DB=devdb -p 5432:5432 postgres:15

2

Check the running containers

Write a Docker command to list all running containers. Use the docker ps command.

Docker

docker run -d --name local-postgres -e POSTGRES_USER=devuser -e POSTGRES_PASSWORD=devpass -e POSTGRES_DB=devdb -p 5432:5432 postgres:15
# Write the command to list running containers
# Your code here

Hint

Use docker ps to see running containers.

3

Filter the running containers to find your PostgreSQL container

Write a Docker command to list running containers but only show the container named local-postgres. Use docker ps with the --filter option and filter by name=local-postgres.

Docker

docker run -d --name local-postgres -e POSTGRES_USER=devuser -e POSTGRES_PASSWORD=devpass -e POSTGRES_DB=devdb -p 5432:5432 postgres:15
docker ps
# Write the command to filter running containers by name 'local-postgres'
# Your code here

Hint

Use docker ps --filter "name=local-postgres" to find your container.

4

Display the container status

Write a command to show only the status of the container named local-postgres. Use docker inspect with the --format option and the Go template {{.State.Status}}.

Docker

docker run -d --name local-postgres -e POSTGRES_USER=devuser -e POSTGRES_PASSWORD=devpass -e POSTGRES_DB=devdb -p 5432:5432 postgres:15
docker ps
docker ps --filter "name=local-postgres"
# Write the command to show the status of 'local-postgres'
# Your code here

Hint

Use docker inspect --format='{{.State.Status}}' local-postgres to see if the container is running.

Practice

1. What is the main benefit of using a database container for local development?

easy

A. You can run a database without installing it on your computer

B. It makes your computer run faster

C. It automatically writes your application code

D. It replaces the need for a database in production

Solution

1. Step 1: Understand what a database container does

   A database container runs a database inside a Docker container, so you don't need to install the database software directly on your computer.

2. Step 2: Identify the main benefit for local development

   This means you can start and stop the database easily without changing your computer setup.

3. Final Answer:

   You can run a database without installing it on your computer -> Option A

4. Quick Check:

   Database container = no local install needed [OK]

Hint: Containers run databases isolated, no install needed [OK]

Common Mistakes:

• Thinking containers speed up the computer
• Confusing containers with code generators
• Believing containers replace production databases

2. Which Docker command correctly starts a PostgreSQL database container exposing port 5432?

easy

A. docker build -p 5432 postgres

B. docker start -p 5432 postgres

C. docker create postgres -p 5432:5432

D. docker run -d -p 5432:5432 postgres

Solution

1. Step 1: Identify the correct command to run a container with port mapping

   The command to start a container and map ports is docker run -d -p hostPort:containerPort image. Here, -d runs it in the background.

2. Step 2: Check each option

   docker run -d -p 5432:5432 postgres uses docker run -d -p 5432:5432 postgres, which is correct. docker start -p 5432 postgres uses docker start which does not support -p. docker create postgres -p 5432:5432 uses docker create which creates but does not start the container. docker build -p 5432 postgres uses docker build which builds images, not runs containers.

3. Final Answer:

   docker run -d -p 5432:5432 postgres -> Option D

4. Quick Check:

   Run + port mapping = docker run -d -p [OK]

Hint: Use 'docker run -d -p host:container image' to start with ports [OK]

Common Mistakes:

• Using 'docker start' with port flags
• Confusing 'docker create' with 'docker run'
• Using 'docker build' to run containers

3. What will be the output of the command docker ps after running docker run -d -p 3306:3306 --name mysql-db mysql?

medium

A. No containers running

B. An error saying port 3306 is already in use

C. A running container named mysql-db with port 3306 mapped

D. A stopped container named mysql-db

Solution

1. Step 1: Understand what the command does

   The command runs a MySQL container in detached mode (-d), names it mysql-db, and maps port 3306 on the host to port 3306 in the container.

2. Step 2: Predict the output of docker ps

   docker ps lists running containers. Since the container runs detached and should start successfully, it will show a running container named mysql-db with port 3306 mapped.

3. Final Answer:

   A running container named mysql-db with port 3306 mapped -> Option C

4. Quick Check:

   Detached run + docker ps = running container shown [OK]

Hint: Detached run shows container in 'docker ps' list [OK]

Common Mistakes:

• Assuming 'docker ps' shows stopped containers
• Expecting errors without port conflicts
• Confusing 'docker ps' with 'docker ps -a'

4. You tried to start a PostgreSQL container with docker run -d -p 5432:5432 postgres but got an error that port 5432 is already in use. What should you do to fix this?

medium

A. Stop the service using port 5432 or map to a different host port

B. Change the container port to 5433

C. Remove the postgres image and try again

D. Use docker build instead of docker run

Solution

1. Step 1: Understand the port conflict error

   The error means something on your computer is already using port 5432, so Docker cannot map the container's port to it.

2. Step 2: Fix the conflict by stopping the service or changing host port

   You can stop the program using port 5432 or map the container port to a different host port like 5433 using -p 5433:5432.

3. Final Answer:

   Stop the service using port 5432 or map to a different host port -> Option A

4. Quick Check:

   Port conflict fix = stop service or change host port [OK]

Hint: Change host port or stop conflicting service to fix port error [OK]

Common Mistakes:

• Changing container port instead of host port
• Removing image does not fix port conflicts
• Using 'docker build' instead of 'docker run'

5. You want to reset your local MySQL database container to start fresh without losing your data volume. Which Docker command sequence is correct?

hard

A. docker rm mysql-db && docker run -d -p 3306:3306 --name mysql-db mysql

B. docker stop mysql-db && docker rm mysql-db && docker run -d -p 3306:3306 --name mysql-db mysql

C. docker restart mysql-db && docker run mysql

D. docker stop mysql-db && docker run -d -p 3306:3306 --name mysql-db mysql

Solution

1. Step 1: Stop and remove the existing container

   To reset the container, first stop it with docker stop mysql-db and then remove it with docker rm mysql-db. This removes the container but not the data volume.

2. Step 2: Run a new container with the same name and port mapping

   Start a new container with docker run -d -p 3306:3306 --name mysql-db mysql to get a fresh instance connected to the existing data volume.

3. Final Answer:

   docker stop mysql-db && docker rm mysql-db && docker run -d -p 3306:3306 --name mysql-db mysql -> Option B

4. Quick Check:

   Stop + remove + run = reset container without losing volume [OK]

Hint: Stop and remove container before rerunning to reset it [OK]

Common Mistakes:

• Restarting container does not reset it
• Removing container without stopping first
• Running new container without removing old one