itanaskovic · March 21, 2019 12:11 · Nov 27, 2014 · Nov 27, 2014
diff --git a/Some docker examples → docker-examples.md b/Some docker examples → docker-examples.md
diff --git a/Some docker examples b/Some docker examples
@@ -0,0 +1,76 @@
+### Commit, clone a container
+
+To 'clone' a container, you'll have to make an image of that container first, you can do so 
+by "committing" the container. Docker will (by default) *pause* all processes running in the 
+container during commit to preserve data-consistency.
+
+For example;
+
+    docker commit --message="Snapshot of my container" my_container my_container_snapshot:yymmdd
+
+Commit `my_container` as an image called `my_container_snapshot`, and tag it `yymmdd`. The "message" is optional and allows adding some extra info to the image. 
+
+    $ docker images
+
+    REPOSITORY            TAG      IMAGE ID      CREATED        VIRTUAL SIZE
+    my_container_snapshot yymmdd   9496ac4a89a6  5 seconds ago  85.1 MB
+
+To view the "message" we added earlier, inspect the image using `docker inspect [imagename]`, and to get *just* the message provide a `--filter` option. In this case:
+
+    $ docker inspect --format="{{.Comment}}" my_container_snapshot:yymmdd
+    Snapshot of my container
+
+
+You can start a new container from this snapshot;
+
+    docker run --name=my_clone my_container_snapshot:yymmdd
+
+This will start a new container called "my_clone", using the snapshot we created earlier.
+
+
+### Volumes
+
+When dealing with database containers, most containers use a `volume` for data storage. Data in volumes
+is not considered part of the containers filesystem and will therefore **not** be included when committing a
+container (nor will it be when using `docker export` or `docker save`).
+
+To check if a container uses volumes and where they are located, use `docker inspect`. To get just the information about 'volumes', we're providing a `--filter`;
+
+    $ docker inspect --format="{{json .Volumes}}" my_container
+
+    {"/var/lib/mysql":"/var/lib/docker/vfs/dir/8274456ae711beb73de3ba0d969931c260a1bf063088f436fb08eb79b546d21d"}
+
+This container, running mysql, is using a volume for `/var/lib/mysql`, and is stored inside `/var/lib/docker/vfs/dir/8274456ae711beb73de3ba0d969931c260a1bf063088f436fb08eb79b546d21d` on the host filesystem.
+
+### Backing up volume data
+
+To export data inside a volume, use a utility container, for example, to backup the /var/lib/mysql data directory of the example above, do something like this;
+
+    docker run --rm --volumes-from=my_container debian tar cvf - /var/lib/mysql | gzip > mysql-data.tar.gz
+
+This instruction will;
+
+- start a debian container
+- connect to the *volumes* of `my_container` and mount those volumes at the *same* location as inside `my_container` (ie, `/var/lib/mysql`)
+- Tar + Gzip the `/var/lib/mysql` directory to a file called `mysql-data.tar.gz` in the current directory on the host
+- Perform harakiri (it's a "self destructing" container; setting `--rm` will destroy the container after the command has completed)
+
+### Export a database
+
+To *export* a database, again use a utility container containing the tool to backup your data, for example, to backup
+a mysql database;
+
+    docker run --rm --link=my_container:db mysql:latest mysqldump --host=db -u root my_database > my_database_dump.sql
+
+This instruction will;
+
+- start a mysql container (but doesn't start the mysql *server*, because we're providing a different command)
+- establish a link to `my_container` and name that link `db`
+- add an entry to `/etc/hosts` inside the container for the `db` link. This enables us to connect to the linked container by using `db` as hostname.
+- do a `mysqldump` of the database in the *linked* container (using `db` as hostname)
+- export the dump to a file called `my_database_dump.sql` in the current directory
+- delete the container after the command has completed.
+
+### Import the database in a new container
+
+[write]