I do not understand the syntax of docker-compose: "volumes" and "services" - docker

Question

I don't understand the syntax of the docker-compose-file.
First of all
version: '3'
services:
bla:
command: /bin/bash
stdin_open: true
#tty: true
container_name: docker-gulp-template
#restart: always
build: .
ports:
- '80:3000'
volumes:
- ".:/usr/src/html/bla-source"
volumes:
volumes-xyz:
If I execute it with
docker-compose up
It does create a container with the name
docker-gulp-template_bla
But that sounds illogical to me, though. Shouldn't the container be called this way:
bla_docker-gulp-template ?
Why was it solved like this? Does any of you have an example?
And another point:
volumes:
- ".:/usr/src/html/bla-source"
volumes:
volumes-xyz:
Why do I need the second volumes command and how does docker know that the first volume path belongs to the other volumes name?
Thanks in advance

Answer 1

You don't need the volume section.
A volume can be a named volume, created under the top level volumes section, like
volumes:
volumes-xyz:
and mounted under a service with
volumes:
- "volumes-xyz:/usr/src/html/bla-source"
Named volumes are managed by docker (/var/lib/docker/volumes/ on Linux).
Volume can also be anonymous by
volumes:
- "/usr/src/html/bla-source"
- ".:/usr/src/html/bla-source", on the other hand, creates a "bind mount". It's very similar to volume but you can choose its path to create a two-way mapping between your container and the host.