Makefile run same target multiple time concurrently with different option - docker

Question

I wish to build multiple docker images through my makefile. I have a make target looking like this:
docker:
docker build -t service1:latest -f ./service1/Dockerfile .
docker build -t service2:latest -f ./service2/Dockerfile .
...
To gain time, I want to run them in parallel, so I wanted to update my makefile like this:
docker:
docker build -t $(SERVICE):latest -f ./$(SERVICE)/Dockerfile .
And calling it with something which would look like this:
make -j=2 SERVICE=service1 docker SERVICE=service2 docker
But obviously it does not work since there is multiple issues with this.
I was thinking to use the pattern %, but I am not quite sure how to achieve this cleanly.
What would be the right way to achieve this?

Answer 1

You could write something like this:
IMAGES = \
service1 \
service2
all: $(IMAGES)
.PHONY: $(IMAGES)
$(IMAGES):
docker build -t $#:latest -f $#/Dockerfile .
The .PHONY directive is necessary because otherwise it will find the directory named service1 or service2 and decide that the target does not need updating. .PHONY tells it to ignore this and build the target in any case.
Using this Makefile, if I run make -j it spawns to build processes in parallel.
While this works, I'm not sure that make is really the right tool for the job. The idea behind make is that it will only rebuild those things that need to be rebuilt, saving time if only a few things have been modified.
In this situation, make doesn't really have any way to make that sort of decisions.
Since you want to rebuild everything every time, you might be better off with a simple shell script and xargs:
#!/bin/bash
seq 2 |
xargs -iSERVICENUM -P0 docker build -t serviceSERVICENUM -f serviceSERVICENUM/Dockerfile .
Or if your services aren't actually named in a numeric sequence:
#!/bin/bash
SERVICES='
foo
bar
'
xargs -iSERVICE -P0 docker build -t SERVICE -f SERVICE/Dockerfile . <<<$SERVICES