Wait for multiple services

[andrewshawcare]

It would be ideal if multiple services (i.e. multiple host:port combinations) could be declared such that the command is executed only after all dependent services are available.

[vishnubob]

I feel like this is better solved by either a top level script that orchestrates the logic of such a situation or chaining multiple wait-for-it commands together.

[andrewshawcare]

Yeah, I did that but that approach is potentially misleading.

For example:

./wait-for-it.sh service-a:1234 -- ./wait-for-it.sh service-b:1234 -- docker-entrypoint.sh

Logically, is service-b dependent on service-a? In my case it isn't (so they shouldn't be chained). In my view, it would be clearer to have:

./wait-for-it.sh service-a:1234 service-b:1234 -- docker-entrypoint.sh

Structurally, there should be two options:

container -> {service-a, service-b} // set denotes mutually-exclusive dependencies

container -> [service-a, service-b] // list denotes dependency order

A chain provides a list mechanism and multiple host:port arguments provides a set mechanism.

[vishnubob]

A high-level script is your best option to solving this particular use case, as it allows you the flexibility you need in testing and interpreting the various states that arise in your specific scenario. wait-for-it is intentionally designed to keep-it-simple, leaving the use-case you describe as an exercise for the reader. Feel free to fork and tailor to your needs.

[jlordiales]

@vishnubob did you get to implement your use case? I was looking to do exactly the same

[vishnubob]

@jlordiales: i think you meant to ask @andrewshawcare, since he originally posted the issue.

[jlordiales]

Yes @vishnubob, sorry it was late :)

[jlordiales]

@andrewshawcare FWIW I implemented this on https://github.com/jlordiales/wait-for-it/blob/master/wait-for-it.sh (for my use case at least). You can specify multiple host:port pairs and the whole thing will fail as soon as the first host times out

[Forever-Young]

Didn't see this issue, also implemented this: Forever-Young@f9aa0c1

[frastel]

Could this issue be closed as "won't fix" so it is clear that this high-level functionality shouldn't be integrated in this project?
As vishnubob already mentioned it makes totally sense to keep this script as simple as possible and to not patch this script for this reason.

[Forever-Young]

I guess it's enough to have some receipts just in the issue comments.

[clarketm]

There is a python version of wait-for-it that supports waiting for multiple services. It is blocking and will wait for the services to be available in sequential order.

e.g.

Assuming both python3 and wait-for-it are installed.

$ wait-for-it \
--service www.google.com:80 \
--service www.bing.com:80 \
--service www.duckduckgo.com:80 \
-- echo "google, bing, and duckduckgo are up (in that order)"

Here are the docs!

[Feche-314]

There is also a shell script called docker-compose-wait which allows this required behaviour:

version: "3"

services:
  mongo:
    image: mongo:3.4
    hostname: mongo
    ports:
      - "27017:27017"

  postgres:
    image: "postgres:9.4"
    hostname: postgres
    ports:
      - "5432:5432"

  mysql:
    image: "mysql:5.7"
    hostname: mysql
    ports:
      - "3306:3306"

  mySuperApp:
    image: "mySuperApp:latest"
    hostname: mySuperApp
    environment:
      WAIT_HOSTS: postgres:5432, mysql:3306, mongo:27017

[codan84]

There is also a shell script called docker-compose-wait which allows this required behaviour:

version: "3"

services:
  mongo:
    image: mongo:3.4
    hostname: mongo
    ports:
      - "27017:27017"

  postgres:
    image: "postgres:9.4"
    hostname: postgres
    ports:
      - "5432:5432"

  mysql:
    image: "mysql:5.7"
    hostname: mysql
    ports:
      - "3306:3306"

  mySuperApp:
    image: "mySuperApp:latest"
    hostname: mySuperApp
    environment:
      WAIT_HOSTS: postgres:5432, mysql:3306, mongo:27017

Thanks for this tip, much better imo and not dependant on bash present in the image