[Bug] Global output parameters validation error with reversed dag.tasks order

[cy-zheng]

Summary

What happened/what you expected to happen?

A workflow using global output parameter and DAG could work well with Argo, but if I reverse the dag.tasks list, argo server would return a global output parameters validation error like:

{
    "code": 2,
    "message": "templates.dag.tasks.second templates.second: failed to resolve {{workflow.outputs.parameters.first-global-name}}"
}

Expection:
Parameter verification should not be related to DAG tasks' order.

Diagnostics

What Kubernetes provider are you using?

Bare-metal v1.13.12

What version of Argo Workflows are you running?

v2.11.3

The workflow works well:

POST {argo-server}/api/v1/workflows/test4
{
    "namespace":"test4",
    "workflow":{
        "metadata":{
            "name":"workflow-works-well",
            "namespace":"test4"
        },
        "spec":{
            "templates":[
                {
                    "name":"dag",
                    "dag":{
                        "tasks":[
                            {
                                "name":"first",
                                "template":"first"
                            },
                            {
                                "name":"second",
                                "template":"second",
                                "dependencies":[
                                    "first"
                                ]
                            }
                        ]
                    }
                },
                {
                    "name":"first",
                    "container":{
                        "name":"test",
                        "image":"ubuntu",
                        "command":[
                            "sh",
                            "-c",
                            "echo first > /tmp/empty-dir/output.txt"
                        ],
                        "volumeMounts":[
                            {
                                "mountPath":"/tmp/empty-dir",
                                "name":"output"
                            }
                        ]
                    },
                    "outputs":{
                        "parameters":[
                            {
                                "name":"first-output",
                                "valueFrom":{
                                    "path":"/tmp/empty-dir/output.txt"
                                },
                                "globalName":"first-global-name"
                            }
                        ]
                    },
                    "volumes":[
                        {
                            "name":"output",
                            "emptyDir":{

                            }
                        }
                    ]
                },
                {
                    "name":"second",
                    "container":{
                        "name":"test",
                        "image":"ubuntu",
                        "command":[
                            "sh",
                            "-c",
                            "echo {{workflow.outputs.parameters.first-global-name}}"
                        ]
                    }
                }
            ],
            "entrypoint":"dag",
            "serviceAccountName":"workflow"
        }
    }
}

The workflow suffers from a validation error:

POST {argo-server}/api/v1/workflows/test4
{
    "namespace":"test4",
    "workflow":{
        "metadata":{
            "name":"workflow-error",
            "namespace":"test4"
        },
        "spec":{
            "templates":[
                {
                    "name":"dag",
                    "dag":{
                        "tasks":[
                            {
                                "name":"second",
                                "template":"second",
                                "dependencies":[
                                    "first"
                                ]
                            },
                            {
                                "name":"first",
                                "template":"first"
                            }
                        ]
                    }
                },
                {
                    "name":"first",
                    "container":{
                        "name":"test",
                        "image":"ubuntu",
                        "command":[
                            "sh",
                            "-c",
                            "echo first > /tmp/empty-dir/output.txt"
                        ],
                        "volumeMounts":[
                            {
                                "mountPath":"/tmp/empty-dir",
                                "name":"output"
                            }
                        ]
                    },
                    "outputs":{
                        "parameters":[
                            {
                                "name":"first-output",
                                "valueFrom":{
                                    "path":"/tmp/empty-dir/output.txt"
                                },
                                "globalName":"first-global-name"
                            }
                        ]
                    },
                    "volumes":[
                        {
                            "name":"output",
                            "emptyDir":{

                            }
                        }
                    ]
                },
                {
                    "name":"second",
                    "container":{
                        "name":"test",
                        "image":"ubuntu",
                        "command":[
                            "sh",
                            "-c",
                            "echo {{workflow.outputs.parameters.first-global-name}}"
                        ]
                    }
                }
            ],
            "entrypoint":"dag",
            "serviceAccountName":"workflow"
        }
    }
}

The only different thing is the order of dag.tasks.

Paste the logs from the argo-server:
kubectl logs argo-server-6d5dd8655d-bh9dj -n argo

time="2020-10-14T12:11:04Z" level=error msg="finished unary call with code Unknown" error="templates.dag.tasks.second templates.second: failed to resolve {{workflow.outputs.parameters.first-global-name}}" grpc.code=Unknown grpc.method=CreateWorkflow grpc.service=workflow.WorkflowService grpc.start_time="2020-10-14T12:11:04Z" grpc.time_ms=0.322 span.kind=server system=grpc

---

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[alexec]

By the sounds of this, you can work-around by re-ordering tasks.

[cy-zheng]

By the sounds of this, you can work-around by re-ordering tasks.

Yes. I've tested that reordering works well in all of my cases, and I need to add some topology sorting logic before submitting a workflow to argo.

By the way, is this behavior an expectation of argo? Will it be fixed in a future version?

Thanks for your quick response! @alexec

[alexec]

Well, it is software, so it has bugs. Would you like to submit a PR to fix?

[cy-zheng]

Well, it is software, so it has bugs. Would you like to submit a PR to fix?

I'll do more investigation and try to find causes on argo side.

I would try to fix it if I could.

[alexec]

Merged into https://github.com/argoproj/argo/releases/tag/v2.12.0-rc4