instruction: Explain Persisting container data
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  Explanation
  When a container starts, it uses the files and configuration provided by the image. Each container is able to create, modify, and delete files and does so without affecting any other containers. When the container is deleted, these file changes are also deleted.
  While this ephemeral nature of containers is great, it poses a challenge when you want to persist the data. For example, if you restart a database container, you might not want to start with an empty database. So, how do you persist files?
  Container volumes
  Volumes are a storage mechanism that provide the ability to persist data beyond the lifecycle of an individual container. Think of it like providing a shortcut or symlink from inside the container to outside the container.
  As an example, imagine you create a volume named
  log-data
  docker volume create log-data
  When starting a container with the following command, the volume will be mounted (or attached) into the container at
  /logs
  docker run -d -p 80:80 -v log-data:/logs docker/welcome-to-docker
  If the volume
  log-data
  doesn't exist, Docker will automatically create it for you.
  When the container runs, all files it writes into the
  /logs
  folder will be saved in this volume, outside of the container. If you delete the container and start a new container using the same volume, the files will still be there.
  Sharing files using volumes
  You can attach the same volume to multiple containers to share files between containers. This might be helpful in scenarios such as log aggregation, data pipelines, or other event-driven applications.
  Managing volumes
  Volumes have their own lifecycle beyond that of containers and can grow quite large depending on the type of data and applications youâre using. The following commands will be helpful to manage volumes:
  docker volume ls
  - list all volumes
  docker volume rm <volume-name-or-id>
  - remove a volume (only works when the volume is not attached to any containers)
  docker volume prune
  - remove all unused (unattached) volumes
  Try it out
  In this guide, youâll practice creating and using volumes to persist data created by a Postgres container. When the database runs, it stores files into the
  /var/lib/postgresql/data
  directory. By attaching the volume here, you will be able to restart the container multiple times while keeping the data.
  Use volumes
  Download and install
  Docker Desktop.
  Start a container using the
  Postgres image
  with the following command:
  docker run --name
  db -e
  POSTGRES_PASSWORD
  secret -d -v postgres_data:/var/lib/postgresql/data postgres
  This will start the database in the background, configure it with a password, and attach a volume to the directory PostgreSQL will persist the database files.
  Connect to the database by using the following command:
  docker
  exec
  -ti db psql -U postgres
  In the PostgreSQL command line, run the following to create a database table and insert two records:
  CREATE TABLE tasks (
  id SERIAL PRIMARY KEY,
  description VARCHAR(100)
  INSERT INTO tasks (description) VALUES ('Finish work'), ('Have fun');
  Verify the data is in the database by running the following in the PostgreSQL command line:
  SELECT * FROM tasks;
  You should get output that looks like the following:
  id | description
  1 | Finish work
  2 | Have fun
  (2 rows)
  Exit out of the PostgreSQL shell by running the following command:
  Stop and remove the database container. Remember that, even though the container has been deleted, the data is persisted in the
  postgres_data
  volume.
  docker stop db
  docker rm db
  Start a new container by running the following command, attaching the same volume with the persisted data:
  docker run --name
  new-db -d -v postgres_data:/var/lib/postgresql/data postgres
  You might have noticed that the
  POSTGRES_PASSWORD
  environment variable has been omitted. Thatâs because that variable is only used when bootstrapping a new database.
  Verify the database still has the records by running the following command:
  docker
  exec
  -ti new-db psql -U postgres -c
  "SELECT * FROM tasks"
  View volume contents
  The Docker Desktop Dashboard provides the ability to view the contents of any volume, as well as the ability to export, import, and clone volumes.
  Open the Docker Desktop Dashboard and navigate to the
  Volumes
  view. In this view, you should see the
  postgres_data
  volume.
  Select the
  postgres_data
  volumeâs name.
  Data
  tab shows the contents of the volume and provides the ability to navigate the files. Double-clicking on a file will let you see the contents and make changes.
  Right-click on any file to save it or delete it.
  Remove volumes
  Before removing a volume, it must not be attached to any containers. If you havenât removed the previous container, do so with the following command (the
  will stop the container first and then remove it):
  docker rm -f new-db
  There are a few methods to remove volumes, including the following:
  Select the
  Delete Volume
  option on a volume in the Docker Desktop Dashboard.
  Use the
  docker volume rm
  command:
  docker volume rm postgres_data
  Use the
  docker volume prune
  command to remove all unused volumes:
  docker volume prune
  Additional resources
  The following resources will help you learn more about volumes:
  Manage data in Docker
  Volumes
  Volume mounts
  Next steps
  Now that you have learned about persisting container data, itâs time to learn about sharing local files with containers.
  Sharing local files with containers