README.md

TMPFS mounts

TMPFS mount are intended to store data in an ephemeral way, meaning that when the container stops, all the data vanish.

So why not storing data within the container's RW layer? To prevent the container growing in size.

The typical data that you can afford to miss (in some situations) are the log files; let's try to store nginx log files in an TMPFS mounted volume.

Prerequisites

Having completed lab 00 - Setup lab environment

Connect to Sunnyvale's Ubuntu VM

$ cd <GIT_REPO_NAME>/vagrant
$ vagrant up
$ vagrant ssh
vagrant@docker-vm:~$ 

## Run the container with a TMPFS-mounted volume

vagrant@docker-vm:~$ docker run \
    -d \
    -p 4000:80 \
    --mount type=tmpfs,destination=/var/log/nginx \
    nginx:latest
9cb9e3039259e116a4c190b80a81be89408446fe6b89b515c6d3fbceb49832a2

Let's make the nginx log something

vagrant@docker-vm:~$ for i in {1..50000} 
    do 
        curl -s http://localhost:4000 
    done

After a while, by attaching to the nginx container to run the ls -lh command, we get the dimension of the access.log

vagrant@docker-vm:~$ docker exec 9cb9e3039259e116a4c190b80a81be89408446fe6b89b515c6d3fbceb49832a2 ls -lh /var/log/nginx/access.log
-rw-r--r-- 1 root root 411K Oct 26 14:18 /var/log/nginx/access.log

If you stop the container

vagrant@docker-vm:~$ docker stop 9cb9e3039259e116a4c190b80a81be89408446fe6b89b515c6d3fbceb49832a2

And you start it over

vagrant@docker-vm:~$ docker start 9cb9e3039259e116a4c190b80a81be89408446fe6b89b515c6d3fbceb49832a2

You will see that the dimension of the access.log file is 0. It means that the TMPFS-mounted volume has been discarded and recreated empty.

vagrant@docker-vm:~$ docker exec 9cb9e3039259e116a4c190b80a81be89408446fe6b89b515c6d3fbceb49832a2 ls -lh /var/log/nginx/access.log
-rw-r--r-- 1 root root 0 Oct 26 14:18 /var/log/nginx/access.log

Finally you can stop the container

vagrant@docker-vm:~$ docker stop 9cb9e3039259e116a4c190b80a81be89408446fe6b89b515c6d3fbceb49832a2

and remove it

vagrant@docker-vm:~$ docker rm 9cb9e3039259e116a4c190b80a81be89408446fe6b89b515c6d3fbceb49832a2

NOTE: we used the hash 9cb9e3039259e116a4c190b80a81be89408446fe6b89b515c6d3fbceb49832a2 to reference the running container, this value is different in your environment so please change this value with yours accordingly.