ENTRYPOINT & CMD commands with mongod results in unknown option error

Question

I am using multiple Dockerfiles to setup my server infrastructure. One of the Dockerfiles I build is a MongoDB server which will be linked to a running web server application in a later step. Currently, I have the problem when running the MongoDB server I receive following error:

"Error parsing command line: unknown option port 27017"

In my Dockerfile I have:

CMD ["--port 27017", "--dbpath /data/db", "--smallfiles"]    
ENTRYPOINT ["/usr/bin/mongod"]

When I use instead of the above commands the following everything works:

CMD /usr/bin/mongod --port 27017 --dbpath /data/db --smallfiles

I prefer the CMD - Array and ENTRYPOINT approach more but cannot figure out why I receive the error.

Answer 1

When using the json syntax, you need to pass each argument individually. It will consider each element as one whereas in the non-json syntax, it will be split by the shell and considered as two.

CMD ["--port", "27017", "--dbpath", "/data/db", "--smallfiles"] will work.

Alternatively, I don't know if mongo supports it, but most softwares does, you could do this:

CMD ["--port=27017", "--dbpath=/data/db", "--smallfiles"] so it will get passed as one element but will be interpreted by mongo.