chore: volumes for postgres

.github/README.md

@@ -8,8 +8,9 @@ My Dockerfiles & docker-compose files that tested
 
 ## Docs
 
-- [PostgreSQL](./docs/postgresql.md).
-- [Choosing the right image](./docs/choose-the-right-image.md).
+- [PostgreSQL](../docs/docs/postgresql.md).
+- [Choosing the right image](../docs/docs/choose-the-right-image.md).
+- [Docker volumes](../docs/volumes.md).
 
 # Tips:
 

docker-compose-files/postgres/postgres-pgadmin/compose.yml

@@ -5,7 +5,7 @@ services:
     ports:
       - "${POSTGRESQL_EXPOSED_PORT}:5432"
     volumes:
-      - /data/postgres:/data/postgres
+      - postgres:${PGDATA}
     env_file:
       - .env
     healthcheck:
@@ -60,3 +60,6 @@ configs:
           }
         }
       }
+
+volumes:
+  postgres:

docker-compose-files/postgres/postgres-pgadmin/test-persistence.py

@@ -0,0 +1,28 @@
+import psycopg
+
+# Connect to an existing database
+with psycopg.connect("dbname=db-name host=localhost password='change-me' user=username") as connection:
+    # Open a cursor to perform database operations
+    with connection.cursor() as cursor:
+        cursor.execute("""
+            CREATE TABLE IF NOT EXISTS tests (
+                id UUID PRIMARY KEY,
+                name VARCHAR(255)
+            )""")
+        cursor.execute("""
+                INSERT INTO public.tests
+                VALUES (gen_random_uuid(), %(name)s)
+            """, {
+                "name": "Mohammad Jawad (Kasir)"
+            })
+        cursor.execute("""
+            SELECT *
+            FROM public.tests
+        """)
+
+        record = cursor.fetchone()
+
+        print(record)
+
+        # Make the changes to the database persistent
+        connection.commit()

docs/volumes.md

@@ -0,0 +1,26 @@
+# Docker volumes
+
+How you ever wondered how docker volumes work? Let's jump into it real quick.
+
+## Mechanics behind docker volumes
+
+- A special type of storage in docker.
+- Designed to **persist** data independent of the container lifecycle.
+  - The idea is that when a container stops, crashes, or is deleted, the data stored in the volume remains intact **as long as the volume itself is not deleted**.
+- Gives you data isolation.
+- Bind mount:
+  - Directly maps a host (your local system filesystem) directory, into a docker volume.
+- Volume:
+  - Is managed by docker and stored in docker's storage directory (e.g., `/var/lib/docker/volumes` on Linux).
+
+## Compose files
+
+- E.g. in [this compose file](../docker-compose-files/postgres/postgres-pgadmin/compose.yml) we Map a named volume (i.e. `postgres`) to the container path `/var/lib/postgresql/data/pgdata`.
+
+  That is where PostgreSQL stores its data files by default ([ref](https://github.com/docker-library/docs/blob/master/postgres/README.md#pgdata)). This ensures PostgreSQL's database files are written to the volume.
+
+- To test it:
+  1. Run [this python script](../docker-compose-files/postgres/postgres-pgadmin/test-persistence.py).
+  2. `docker compose down`. Do NOT pass `-v` flag since it will delete the volume along side the data.
+  3. `docker compose up -d`.
+  4. Check your database to see if everything is there.

index.md

@@ -4,8 +4,9 @@ My Dockerfiles & docker-compose files that tested
 
 ## Docs
 
-- [PostgreSQL](./.github/docs/postgresql.md).
-- [Choosing the right image](./.github/docs/choose-the-right-image.md).
+- [PostgreSQL](./docs/docs/postgresql.md).
+- [Choosing the right image](./docs/docs/choose-the-right-image.md).
+- [Docker volumes](./docs/volumes.md).
 
 # Tips: