Meaning of ampersand (&) in docker-compose.yml file

I recently came across this and was wondering what &django means

version: '2'

services:
  django: &django

I can't see anything in the docs related to this.

These are a YAML feature called anchors, and are not particular to Docker Compose. I would suggest you have a look at below URL for more details

https://learnxinyminutes.com/docs/yaml/

Follow the section EXTRA YAML FEATURES

> YAML also has a handy feature called 'anchors', which let you easily duplicate > content across your document. Both of these keys will have the same value:

>anchored_content: &anchor_name This string will appear as the value of two keys. other_anchor: *anchor_name

Anchors can be used to duplicate/inherit properties

base: &base
    name: Everyone has same name

foo: &foo
    <<: *base
    age: 10

bar: &bar
    <<: *base
    age: 20

To complement Tarun's answer, & identifies an anchor and * is an alias referring back to the anchor. It is described as the following in the YAML specification:

> In the representation graph, a node may appear in more than one > collection. When serializing such data, the first occurrence of the > node is identified by an anchor. Each subsequent occurrence is > serialized as an alias node which refers back to this anchor.

Sidenote:

For those who want to start using anchors in your docker-compose files, there is more powerful way to make re-usable anchors by using docker-compose YAML extension fields.

version: "3.4"

# x-docker-data is an extension and when docker-compose
# parses the YAML, it will not do anything with it

x-docker-data: &docker-file-info
  build:
    context: .
    dockerfile: Dockerfile

services:
  some_service_a:
    <<: *docker-file-info
    restart: on-failure
    ports:
      - 8080:9090
  some_service_b:
    <<: *docker-file-info
    restart: on-failure
    ports:
      - 8080:9595