Database containers for local development in Docker - Step-by-Step Execution

Process Flow - Database containers for local development

Write Docker run command for DB container

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Docker pulls DB image if not present

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Docker creates and starts container

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DB container runs locally

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Connect app to DB container via port

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Develop and test locally with DB

This flow shows how to start a database container locally using Docker, then connect your app to it for development and testing.

Execution Sample

Docker

docker run --name local-postgres -e POSTGRES_PASSWORD=pass123 -p 5432:5432 -d postgres

Starts a PostgreSQL database container locally with password and port mapping.

Process Table

Step	Action	Docker Output	Container State	Notes
1	Run docker command to start DB container	Unable to find image 'postgres:latest' locally latest: Pulling from library/postgres Digest: sha256:... Status: Downloaded newer image for postgres:latest	Container created but starting	Docker pulls image because not found locally
2	Docker creates and starts container	a1b2c3d4e5f6g7h8i9j0	Running	Container ID shown, DB server starting inside container
3	Container listens on port 5432	No output	Running	Port 5432 on host mapped to container's 5432
4	Connect app to DB at localhost:5432	No output	Running	App can now connect to DB using password 'pass123'
5	Stop container when done	local-postgres	Stopped	Container stopped, DB no longer accessible
6	Exit	N/A	N/A	Development session ends

💡 Container stopped or user ends session, DB container no longer running

Status Tracker

Variable	Start	After Step 1	After Step 2	After Step 3	After Step 5
Container State	Not created	Image pulled, container created	Running	Running and listening on port	Stopped
DB Accessibility	No	No	Yes	Yes	No

Key Moments - 3 Insights

Why does Docker pull the image before creating the container?

Docker needs the database image locally to create a container. If it's not found, it downloads it first as shown in execution_table step 1.

How does the app connect to the database inside the container?

The port mapping (-p 5432:5432) makes the container's DB port accessible on localhost:5432, so the app connects there as in step 4.

What happens if you stop the container?

Stopping the container stops the database server, so the app can no longer connect, as shown in step 5.

Visual Quiz - 3 Questions

Look at the execution_table, what is the container state after step 2?

A Created but not running

B Stopped

C Running

D Not created

💡 Hint

Check the 'Container State' column in row for step 2.

At which step does the database become accessible to the app?

A Step 1

B Step 3

C Step 5

D Step 6

💡 Hint

Look for 'DB Accessibility' becoming 'Yes' in variable_tracker after steps.

If you omit the -p 5432:5432 option, what changes in the execution?

A App cannot connect to DB on localhost

B Container will not start

C DB password will be ignored

D Image will not be pulled

💡 Hint

Port mapping controls access from host to container; see step 3 notes.

Concept Snapshot

Use 'docker run' with DB image to start a local DB container.
Map container port to host port with '-p' for app access.
Set environment variables like POSTGRES_PASSWORD for DB setup.
Container runs isolated but accessible via mapped ports.
Stop container to end local DB session.

Full Transcript

This visual execution shows how to use Docker to run a database container locally for development. First, you run a docker command that pulls the database image if not present. Then Docker creates and starts the container, which runs the database server inside. The container port is mapped to the host port so your app can connect to the database at localhost. You can develop and test your app using this local database. When done, stopping the container stops the database server and closes access. Key points include image pulling, container creation, port mapping, and container lifecycle.