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From Daniel Imberman <daniel.imber...@gmail.com>
Subject Re: Simplifying the KubernetesExecutor
Date Wed, 12 Aug 2020 19:42:39 GMT
I think pod_mutation is important as an “admin override”. E.g. there might be a label that
is required by security policy for all tasks launched by airflow. I do agree that the executor_config
should take in a V1Pod object

One option is that the executor_config could take in a pod_mutation_hook function as well?
So users can manually override the pod functionally rather than just giving an object and
hoping it merges the way they expect it to?
via Newton Mail [https://cloudmagic.com/k/d/mailapp?ct=dx&cv=10.0.50&pv=10.15.5&source=email_footer_2]
On Wed, Aug 12, 2020 at 12:19 PM, David Lum <davidlum91@gmail.com> wrote:
I'll just leave some passing thoughts here. How the pod template file is
modified by the executor config might not be very well defined. Currently
when a user passes in a k8s.V1Pod object through executor_config we kind of
arbitrarily merge the two pod definitions to what we imagine the client
would want, but it could be often misinterpreted. Previously the
Airflow-defined Pod class was fairly flat. This made merging the two
objects fairly straight forward. If the user wrote the field in
executor_config, it overwrote that field in the Pod definition, but the
rest stayed the same. When attributes are arbitrarily nested like in the
k8s.V1Pod, some aspects can be mistakenly overwritten. For example,
specifying the volumeMounts of a container requires also specifying the
rest of the V1Pod. How do we handle this? Do we just overwrite
volumeMounts? The client must have specified a container, so do we
overwrite that too? The fact that there is a choice means the API could be
unintuitive to the user.

What I suggest might be easier is that executor_config completely replaces
the pod_template_file if it is specified, but then also offer something
like pod_mutation_hook at the operator level. This makes it quite clear to
the user, you are either replacing the pod_template, or you are modifying
the pod_template with pod_mutation_hook and you are doing it by your own
rules. the argument to executor_config can be something like
```
executor_config: { 'KubernetesExector': {'pod_mutation': some_func,
'pod_template': k8s.V1Pod(...) }} # Pod template could also be a path to a
file
```

If both are specified then pod_mutation is a function applied to
pod_template. Thoughts?

On Wed, Aug 12, 2020 at 11:24 AM Tomasz Urbaszek <turbaszek@apache.org>
wrote:

> +1 for the idea, thanks Daniel! I agree that multi-executor and pod
> templates should be 2.1.
>
> T.
>
> On Wed, Aug 12, 2020 at 5:13 PM Daniel Imberman <daniel.imberman@gmail.com>
> wrote:
>
>> (Also funny enough we could use a lot of the existing infrastructure int
>> 1.10 to create that migration script. Would just need to take the python
>> dictionary and use the python yaml library)
>>
>> via Newton Mail [
>> https://cloudmagic.com/k/d/mailapp?ct=dx&cv=10.0.50&pv=10.15.5&source=email_footer_2
>> ]
>> On Wed, Aug 12, 2020 at 8:09 AM, Daniel Imberman <
>> daniel.imberman@gmail.com> wrote:
>> 100% agreed on timing. I think 2.0 should be for the breaking aspect
>> (losing the configurations) and then 2.1/2.2 we can start adding on the new
>> features. I also like the idea of a migration tool. We can make a script
>> that takes your airflow.cfg and converts that into a yaml file.
>>
>> via Newton Mail [
>> https://cloudmagic.com/k/d/mailapp?ct=dx&cv=10.0.50&pv=10.15.5&source=email_footer_2
>> ]
>> On Wed, Aug 12, 2020 at 7:48 AM, Jarek Potiuk <Jarek.Potiuk@polidea.com>
>> wrote:
>> Big +1. All the arguments are very appealing to me and simplifying the
>> Kubernetes Executor down to YAML-configurable one seems like a no-brainer
>> especially if we provide some migration tools. I've lost countless hours
>> on
>> debugging some configuration problems, simply because the relevant
>> Kubernetes-related configuration was in the least expected place - i.e.
>> airflow.cfg. YAML configuration.
>>
>> I am also a big fan of both 1. and 2. I've implemented a POC of
>> queue-based multi-scheduler once but having it embedded as part of core
>> Airflow rather than based it on queues (which are basically a Celery
>> Executor concept) is I think much better approach. Both 1. and 2. are
>> cool.
>>
>> Now - question about timing. If we decide to go that route - my view is
>> that simplifying Kubernetes should be an Airflow 2.0 task - alongside more
>> comprehensive tests (which will be much easier to write in this case). The
>> new features/ideas 1. 2. for KE I think should come after that - when we
>> release and stabilize 2.0. Sounds like great candidates for 2.1 to me.
>>
>> J.
>>
>>
>> On Wed, Aug 12, 2020 at 4:24 PM Daniel Imberman <
>> daniel.imberman@gmail.com>
>> wrote:
>>
>> > Hello, fellow Airflowers! I hope you are all well in these trying times.
>> >
>> >
>> > With the recent launch of Airflow 2.0 preparation, it now seems like a
>> > good time to review the project's state and where we can fit in some
>> > breaking changes that will improve the project for the future.
>> >
>> >
>> > When we first created the KubernetesExecutor, we had two goals in mind.
>> > The first goal was to improve the airflow Auto scaling story.
>> Previously,
>> > airflow users would have to manually provision celery workers, which
>> could
>> > lead to wasted resources or missed SLAs. The other goal was to
>> introduce a
>> > community that was not yet well versed in the Kubernetes API to the
>> > Kubernetes system.
>> >
>> >
>> > To ease the community's transition, we abstracted many of the
>> complexities
>> > of creating a Kubernetes object. We chose to offer a limited number of
>> > configurations and keep much of the pod creation process internal to
>> > airflow. In the short-term, this system lowered the barrier to entry.
>> Over
>> > time, however, this abstraction has become a nightmare of tech debt as
>> the
>> > Kubernetes API is expensive and constantly changing.
>> >
>> >
>> > With this in mind, I think it's time for us to consider a more
>> > straightforward approach that takes the complexity out of Airflow and
>> > offers the full Kubernetes API to the airflow user.
>> >
>> >
>> > What I'm proposing here is pretty straightforward. We remove all
>> > Kubernetes pod creation configurations from the airflow.cfg and instead
>> > offer only one way to use the KubernetesExecutor: with a YAML file.
>> >
>> >
>> > We can easily supply all of the configurations to the KubernetesExecutor
>> > by offering example YAMLs (git sync mode is just a sidecar and an init
>> > container, DAG volumes are just an example volume and volume mount,
>> etc.).
>> >
>> >
>> > This system would simplify a user's ability to predict what a pod will
>> > look like once it is launched by airflow. They will know it's a base pod
>> > and will be able to simply modify the pod object using the executor
>> config
>> > and the pod mutation hook.
>> >
>> >
>> >
>> >
>> >
>> >
>> >
>> > This simplification could also lead to some pretty great new features in
>> > the KubernetesExecutor
>> >
>> >
>> > Idea 1: Picking a pod_template_file per-task
>> > Along with the existing customization with the executor config, solely
>> > relying on pod files can allow users to pick the pod template file that
>> > they want to use as their base pod on a per-task basis. An Airflow
>> engineer
>> > could supply several pre-made templates for their data scientists to
>> reduce
>> > the amount of customization an airflow user would need to use.
>> >
>> >
>> > Idea 2: Merging the KubernetesExecutor into the CeleryExecutor
>> > One idea that we've been excited about recently has been the idea of
>> > creating merged Celery and Kubernetes executor. This hybrid executor
>> would
>> > default to launching celery workers with KEDA and would have the option
>> to
>> > launch individual tasks using the Kubernetes executor when a user wants
>> > isolation or customization. Simplifying the Kubernetes executor reduces
>> the
>> > number of fail-points that this merged executor would need to account
>> for.
>> >
>> >
>> >
>> > What would we need to do to implement this?
>> > The good news here is that the hard work has already been done! As of
>> > AIRFLOW-5413 [https://issues.apache.org/jira/browse/AIRFLOW-5413] by
>> > David Lum, airflow already has the ability to use base worker pods on a
>> > template file. This would involve primarily code deletion and very
>> little
>> > new code.
>> >
>> >
>> > Thank you for your time and I look forward to the community’s
>> discussion.
>> >
>> > Daniel
>>
>>
>>
>> --
>>
>> Jarek Potiuk
>> Polidea <https://www.polidea.com/> | Principal Software Engineer
>>
>> M: +48 660 796 129 <+48660796129>
>> [image: Polidea] <https://www.polidea.com/>
>
>
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