Define Connections

Getting services up and running isn't everything - they also need to talk to each other in order to serve their purpose. MonkOS abstracts away the complexity of networking and service discovery by introducing simple MonkScript operators that take care of finding services for you.

---

The consumer

Consider the following Kit:

my stuff.yaml

namespace: mystuff

my-service:
    defines: runnable
    containers:
        my-service:
            image: ubuntu:latest
            environment:
                - <- `DB_ADDR=${db-addr}`
                - <- `DB_PORT=${db-port}`
            bash: <- `echo db at $DB_ADDR:$DB_PORT ; sleep 3600`

    variables:
        db-addr:
            type: string
            value: localhost
        db-port:
            type: int
            value: 21721

Let's assume that the ubuntu:latest image expects environment variables DB_ADDR and DB_PORT to be set. We are setting those environment variables based on control plane variables db-addr and db-port.

Whenever we run mystuff/my-service it will assume that the database is at localhost:21721. Though, in most cases, the database will not be at localhost and running this Kit as it is will end in an error.

The provider mystuff/my-service expects a MongoDB database. MonkOS provides a Kit for this. So we don't really need to define it here. It's on the Hub.

Run MongoDB with:

monk run mongodb/mongodb

The connector

Before running mystuff/my-service we need to tell it where to find the database that is currently running. We will do that by replacing localhost with:

<- get-hostname("mongodb/mongodb", "database")

get-hostname finds and returns the hostname of the target container. It takes two arguments:

1. The path of the target runnable and,
2. the name of the container within that runnable.

The Kit should now look like this:

mystuff.yaml

namespace: mystuff

my-service:
    defines: runnable
    containers:
        my-service:
            image: ubuntu:latest
            environment:
                - <- `DB_ADDR=${db-addr}`
                - <- `DB_PORT=${db-port}`
            bash: <- `echo db at $DB_ADDR:$DB_PORT ; sleep 3600`
    variables:
        db-addr:
            type: string
            value: <- get-hostname("mongodb/mongodb", "database")
        db-port:
            type: int
            value: 21721

The result

Run the new Kit with:

monk load mystuff.yaml
monk run mystuff/my-service

It will automatically find MongoDB that we run earlier. It will also work if you decide to run both runnables as a group:

mygroup.yaml

my-group:
    defines: process-group
    runnable-list:
        - mongodb/mongodb
        - mystuff/my-service

monk load mygroup.yaml
monk run mystuff/my-group