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Trigger Conditions

In the previous sections, you have been dealing with just a single dependency. But, in many cases, you want to wait for multiple events to occur and then trigger a resource which means you need a mechanism to determine which triggers to execute based on set of different event dependencies. This mechanism is supported through conditions.

Note: Whenever you define multiple dependencies in a sensor, the sensor applies a AND operation, meaning, it will wait for all dependencies to resolve before it executes triggers. conditions can modify that behavior.

Prerequisite

Minio server must be set up in the argo-events namespace with a bucket called test and it should be available at minio-service.argo-events:9000.

Conditions

Consider a scenario where you have a Webhook and Minio event-source, and you want to trigger an Argo workflow if the sensor receives an event from the Webhook event-source, but, another workflow if it receives an event from the Minio event-source.

  1. Create the webhook event-source and event-source. The event-source listens to HTTP requests on port 12000.

    kubectl -n argo-events apply -f https://raw.githubusercontent.com/argoproj/argo-events/stable/examples/tutorials/06-trigger-conditions/webhook-event-source.yaml
    
  2. Create the minio event-source. The event-source listens to events of type PUT and DELETE for objects in bucket test.

    kubectl -n argo-events apply -f https://raw.githubusercontent.com/argoproj/argo-events/stable/examples/tutorials/06-trigger-conditions/minio-event-source.yaml
    

Make sure there are no errors in any of the event-sources.

  1. Let's create the sensor. If you take a closer look at the trigger templates, you will notice that it contains a field named conditions, which is a boolean expression contains dependency names. So, as soon as the expression is resolved as true, the corresponding trigger will be executed.

     kubectl -n argo-events apply -f https://raw.githubusercontent.com/argoproj/argo-events/stable/examples/tutorials/06-trigger-conditions/sensor-01.yaml
    
  2. Send a HTTP request to Webhook event-source.

    curl -d '{"message":"this is my first webhook"}' -H "Content-Type: application/json" -X POST http://localhost:12000/example
    
  3. You will notice an Argo worklfow with name group-1-xxxx is created with following output,

     __________________________
    < this is my first webhook >
     --------------------------
        \
         \
          \
                        ##        .
                  ## ## ##       ==
               ## ## ## ##      ===
           /""""""""""""""""___/ ===
      ~~~ {~~ ~~~~ ~~~ ~~~~ ~~ ~ /  ===- ~~~
           \______ o          __/
            \    \        __/
              \____\______/
    
  4. Now, lets generate a Minio event so that we can run group-2-xxxx workflow. Drop a file onto test bucket. The workflow that will get created will print the name of the bucket as follows,

     ______
    < test >
     ------
        \
         \
          \
                        ##        .
                  ## ## ##       ==
               ## ## ## ##      ===
           /""""""""""""""""___/ ===
      ~~~ {~~ ~~~~ ~~~ ~~~~ ~~ ~ /  ===- ~~~
           \______ o          __/
            \    \        __/
              \____\______/
    
  5. Great!! You have now learned how to use conditions. Lets update the sensor with a trigger that waits for both dependencies to resolve. This is the normal sensor behavior if conditions is not defined.

     kubectl -n argo-events apply -f https://raw.githubusercontent.com/argoproj/argo-events/stable/examples/tutorials/06-trigger-conditions/sensor-02.yaml
    

    Send a HTTP request and perform a file drop on Minio bucket as done above. You should get the following output.

     _______________________________
    < this is my first webhook test >
     -------------------------------
        \
         \
          \
                        ##        .
                  ## ## ##       ==
               ## ## ## ##      ===
           /""""""""""""""""___/ ===
      ~~~ {~~ ~~~~ ~~~ ~~~~ ~~ ~ /  ===- ~~~
           \______ o          __/
            \    \        __/
              \____\______/