How to construct a string from a list of variable in an ansible template

I'd like to automatically deploy a prometheus.yml configuration file with Ansible. I need the template to create a string of targets based on a list of kafka brokers.

The list is like so:

broker:
  - kafka1
  - kafka2
  - kafka3
# - ...

I want the configuration file to look like so :

- job_name: "kafka"
  static_configs:
    - targets: ["kafka1:9500","kafka2:9500","kafka3:9500","..."]

I'd like to avoid putting the port number in the variable if possible and I'd like the string to be created no matter the number of brokers in the list.
What's the best way to do this?

You can use the filter product in order to create yourself a list of lists:

broker | product([9500]):
- - kafka1
  - 9500
- - kafka2
  - 9500
- - kafka3
  - 9500

Then use a map to apply the join filter to each of the sub lists with a colon, creating the list of brokers with their port

broker | product([9500]) | map('join', ':'):
- kafka1:9500
- kafka2:9500
- kafka3:9500

Which is your expected list of Kafka brokers with their respective ports.

So, your list of brokers should be created with

- targets: "{{ broker | product([9500]) | map('join', ':') }}"

Resulting in

- targets:
  - kafka1:9500
  - kafka2:9500
  - kafka3:9500

Given the task:

- debug:
    msg:
      - targets: "{{ broker | product([9500]) | map('join', ':') }}"
  vars:
    broker:
      - kafka1
      - kafka2
      - kafka3

This yields:

ok: [localhost] => 
  msg:
  - targets:
    - kafka1:9500
    - kafka2:9500
    - kafka3:9500

Thanks to β.εηοιτ.βε's answer and a bit of searching, I managed to write the following in my template file :

- job_name: "kafka"
  static_configs:
    - targets: [{{ broker | product([9500]) | map('join', ':') | map('to_json') | join(',') }}]

which output was :

- job_name: "kafka"
  static_configs:
    - targets: ["kafka1:9500","kafka2:9500","kafka3:9500"]