Using FIFOs (a.k.a. named pipes) is a handy way for implementing IPC (inter-process communication). Because you can send to or receive from other processes like writing/reading ordinary files. Besides, FIFOs can also be stored in Docker’s volumes. That means we can use FIFOs to communicate between containers. Let’s take a look at a quick example. We’ll create a container that reads from a FIFO and display it.
volume=fifo-ipc-example
docker volume create "$volume"
docker run --rm -it -v ${volume}:/var/run/${volume} debian:11-slim mkfifo /var/run/fifo-ipc-example/message
docker run --rm -it -v ${volume}:/var/run/${volume} debian:11-slim cat /var/run/fifo-ipc-example/message
The docker volume command creates a volume. We’ll use it to share a FIFO file. The first docker run command creates a FIFO file (message) on the volume. The second docker run waits for input to the FIFO. If another process writes to the FIFO, the cat command will display it. Let’s open a new terminal and write something to the FIFO from another container.
volume=fifo-ipc-example
docker run --rm -it -v ${volume}:/var/run/${volume} debian:11-slim bash -c "echo 'Hello.' > /var/run/fifo-ipc-example/message"
Then you will see the string “Hello.” in the first terminal. That’s it. Don’t forget to clean the volume up after you are done.
docker volume rm fifo-ipc-example