When I specify ports in a docker-compose.yml file, is it TCP or UDP?

Question

I know that I can specify the protocol of "ports" in the docker-compose.yml file, but I am unsure what the default protocol is, if no protocol is specified.

Is it TCP? Is it UDP? Both?

I haven't been able to find the answer anywhere (including in the Docker Compose file reference).

Answer 1

by default TCP is used, you can see it launching docker-compose ps

If you want to specify you should add /udp or /tcp like :

ports:
  - "80:80/udp"
  - "80:80/tcp"

Answer 2

In addition to above comment for me docker compose long syntax worked to open udp port ,do also check that your required port is open and available to cater request. https://docs.docker.com/compose/compose-file/compose-file-v3/#ports

ports:
 - target: 18123
   published: 18123
   protocol: UDP
   mode: host