[GitHub] [airflow] drexpp opened a new pull request #6634: This commit fixes [AIRFLOW-6033] UI crashes on "Landing Times"

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drexpp opened a new pull request #6634: This commit fixes [AIRFLOW-6033] UI crashes on "Landing Times"
URL: https://github.com/apache/airflow/pull/6634
 
 
   ### Adding our company to _"Who uses Apache Airflow?"_
   
   Hello everyone, is it possible that our company appears on **_"Who uses Apache Airflow?"_** section? We are a small team working in [Endesa](https://www.endesa.com/), a big spanish electric distributor and part of [Enel](https://www.enel.com/). I wrote some pipelines to automate the ETLs processes we use with Hadoop / Spark, so I believe it would be great for our team.
   
   [Endesa](https://www.endesa.com/) [@drexpp]
   ___
   
   Make sure you have checked _all_ steps below.
   
   ### Jira
   
   - [X] My PR addresses the following Airflow Jira Issue [AIRFLOW-6033](https://issues.apache.org/jira/browse/AIRFLOW-6033) and references them in the PR title.
    
   ### Description
   
   I targeted to v1-10-stable since I think is what @ashb recommended to me in my last PR.
   
   - [X] Here are some details about my PR:
   
   
   Airflow UI will crash in the browser returning "Oops" message and the Traceback of the crashing error.
   
   This is caused by modifying a task_id with a capital/small letter, I will point out some examples that will cause airflow to crash:
   
   task_id = "DUMMY_TASK" to task_id = "dUMMY_TASK"
   task_id = "Dummy_Task" to task_id = "dummy_Task" or "Dummy_task",...
   task_id = "Dummy_task" to task_id = "Dummy_tASk"
   ___
   #### File causing the problem:  https://github.com/apache/airflow/blob/master/airflow/www/views.py (lines 1643 - 1654)
   ```
   for task in dag.tasks:
       y[task.task_id] = []
       x[task.task_id] = []
   
       for ti in task.get_task_instances(start_date=min_date, end_date=base_date):
   
           ts = ti.execution_date
           if dag.schedule_interval and dag.following_schedule(ts):
               ts = dag.following_schedule(ts)
           if ti.end_date:
               dttm = wwwutils.epoch(ti.execution_date)
               secs = (ti.end_date - ts).total_seconds()
               x[ti.task_id].append(dttm)
               y[ti.task_id].append(secs)
   ```
   ___
   
   We can see in first two lines inside the first for loop, how the dictionary x and y is being filled with tasks_id attributes which comes from the actual DAG.
   
   The problem actually comes in the second for loop when you get the task instances from a DAG, I am not sure about this next part and I wish someone to clarify my question about this.
   
   I think that the task instances (ti) received from get_task_instances() function comes from the information stored into the database, that is the reason of crash when you access to "Landing Times" page, is that the x and y where filled with the actual name of the task_id in the DAG and the task_instances' task_id has different name stored causing this problem access to the dictionary.
   
   One of my main questions is how having a different task name (such as changing from "run" to "Run") the function get_task_instances() keeps returning past task instances with different name, such asking instances of Run but returns task instances (ti) with task_id "run"?
   
   ### Error screeshot
   
   How to replicate: 
   
     - Launch airflow webserver -p 8080
     - Go to the Airflow-UI
     - Create an example DAG with a task_id name up to your choice in small letters (ex. "run")
     - Launch the DAG and wait its execution to finish
     - Modify the task_id inside the DAG with the first letter to capital letter (ex. "Run")
     - Refresh the DAG
     - Go to "Landing Times" inside the DAG menu in the UI
     - You will get an "oops" message with the Traceback.
   
   ![error_img](https://i.imgur.com/0tXRDuH.png)
   ____
   ### Tests
   
   - [X] My PR adds the following unit tests __OR__ does not need testing for this extremely good reason:
   
     - I didn't know exactly how to unit test this, if you have any advice I will do a test for it. Other than that, I did test checking that the behaviour was as expected:
       
       - [X] Create DAG and access to Landing Times
       - [X] Modify a task from the created DAG to a completly new name and access to Landing Times
       - [X] Modifying a task with capital/lower letters and accessing to Landing Times
       - [X] Switch to the original name and access to Landing Times
   
   
   ### Commits
   
   - [X] My commits all reference Jira issues in their subject lines, and I have squashed multiple commits if they address the same issue. In addition, my commits follow the guidelines from "[How to write a good git commit message](http://chris.beams.io/posts/git-commit/)":
     1. Subject is separated from body by a blank line
     1. Subject is limited to 50 characters (not including Jira issue reference)
     1. Subject does not end with a period
     1. Subject uses the imperative mood ("add", not "adding")
     1. Body wraps at 72 characters
     1. Body explains "what" and "why", not "how"
   
   ### Documentation
   
   - [X] In case of new functionality, my PR adds documentation that describes how to use it.
     - All the public functions and the classes in the PR contain docstrings that explain what it does
     - If you implement backwards incompatible changes, please leave a note in the [Updating.md](https://github.com/apache/airflow/blob/master/UPDATING.md) so we can assign it to a appropriate release
   
   ### Code Quality
   
   - [X] Passes `flake8`
   

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