While splitting the monolithical Airfllow architecture to pieces sounds good, there is one problem that might be difficult to tackle (or rather impossible unless we change architecture of Airflow significantly) - namely dependencies/requirements.
The way Airflow uses operators is that its operators are already closely coupled with Airflow core. Airflow has to parse all the operators within the same python interpreter/virtual machine as the core Airflow. This means potentially big problem with dependency/requirement handling if we have multiple packages. There are enough common/shared dependencies that various operators use even now to cause occasional headaches even now. We already have quite a challenge with handling dependencies of Airflow and its operators/hooks when they are part of Airflow repo. Currently the problem is that Ariflow sometimes uses outdated dependencies or that some random transient dependencies break Airflow installation. But at we at least have a common dependency list that we work against for all operators. Unfortunately if we split, then the problem will be worse - very quickly some contrib operators will require different dependencies and will not be compatible with Airflow or break Airflow's behaviour. Not mentioning the problem when you want to use hooks from some other "area" in your operator. Currently Hooks are the way how you can speed up development of cross-are behaviour. You implement hooks in some "area" and other "areas" are free or even encouraged to use them. For example exporting from BigQuery to all cloud storages in principle should depend on Hooks for every single Cloud Storage package out there (Google, Azure, AWS). This is even worse than the MySqLToHive case described earlier - very quickly we would end up with totally unmanageable mesh of cross-dependencies. I think to really make Operators independent from Airflow core, we would need to allow the dependencies to be fully isolated - i.e. to allow operators to have different set of dependencies than the core. That's quite impossible with the current Airflow approach where the same operator code is parsed in the core. And the same code is used during execute in worker. And the same code might be used by another operator in form of hook. Unfortunately we are not in the npm <https://npm.github.io/how-npm-works-docs/index.html> world (as Kamil Breguła pointed to me today) where the module loaded handles multiple versions of the same library in the same process. One other questions that bothers me - I believe (please correct me If I am wrong) some of the operators are using some core features of Airflow and are even more tied with the Core. For example it is perfectly fine for the operator to use SQL Alchemy ORM classes of Airflow and run queries/perform updates in the metadata database of Airflow, I believe - as far as I know there is a requirement (I saw this somewhere at least) that Celery or Kubernetes workers need to be able to open a direct database connection to the metadata database of Airflow and there is nothing to prevent the operators to do it. This in essence means that the operator has to depend on many core dependencies/requirements including sqlalchemy, postgres/mysql ....). This can be changed and "forbidden" to use Airflow's core features but it might break compatibility (If I am right about it). We could imagine a different approach - where operator is split to a "Proxy" and "Execute" classes. "Proxy" within Core's interpreter with Core's dependencies, and "Executor" within the worker case. Then each task could run in its own Docker image/Pod on Kubernetes with its own dependencies. But that looks like big, backwards-incompatible change and it still does not solve cross-dependencies between different "areas". For handling cross-area operations we would somehow implement communication between different containers - each having own dependencies. That would be possible in Kubernetes by having single POD with several containers sharing the common data and communicating. Seems possible. It's quite an entertaining idea, but it sounds like Airflow 3.0 already and one that is not really backwards compatible ;). J. On Tue, Jan 8, 2019 at 5:37 PM Tim Swast <sw...@google.com.invalid> wrote: > > I don't see it solving any problem than test speed (which is a big one, > yes) but doesn't reduce the amount of workload on the committers. > > It's about distributed ownership. For example, I'm not a committer in > pandas, but I am the primary maintainer of pandas-gbq. You're right that if > the set of committers is the same for all 24 repos, there isn't all that > much benefit beyond testing speed. > > > Each sub-project would still have to follow the normal Apache voting > process. > > Presumably the set of people that care about the sub-packages will be > smaller. I don't know enough about the Apache voting process to know how > that might affect it. > > Maybe many of the sub-packages can live outside the Apache org? Pandas > keeps the I/O sub-packages in a different org, for example. > > > Google could choose to release a airflow-gcp-operators package now and > tell people to |from gcp.airflow.operators import SomeNewOperator|. > > That's actually part of my motivation for this proposal. I've got some red > tape to get through, but ideally the proposed airflow-google repository in > AIP-8 would actually live in the GoogleCloudPlatform org. > > *Maybe I should decrease the scope of AIP-8 to Google hooks/operators?* > > > There is nothing stopping someone /currently/ creating their own > operators package. > > Hooks still need some support in core, so that connections can be > configured. Also, the fact that so many operators live in the Airflow makes > it seem like an operator is less supported / a hack if it doesn't live > there. > > > How will we ensure that core changes don't break any hooks/operators? > > Pandas does this by running tests in the I/O repos against pandas master > branch in addition to against supported releases. > > > How do we support the logging backends for s3/azure/gcp? > > I don't see any reason we can't keep doing what we're already doing. > > > https://github.com/apache/airflow/blob/5d75028d2846ed27c90cc4009b6fe81046752b1e/airflow/utils/log/gcs_task_handler.py#L45 > > We'd need to adjust the import path for the hook, but so long as the upload > / download method remains stable, it'll work the same. The sub-package will > need to ensure it tests the logging code path in addition to testing DAGs > that use the relevant operators. > > * • **Tim Swast* > * • *Software Friendliness Engineer > * • *Google Cloud Developer Relations > * • *Seattle, WA, USA > > > On Tue, Jan 8, 2019 at 7:55 AM Ash Berlin-Taylor <a...@apache.org> wrote: > > > Can someone explain to me how having multiple packages will work in > > practice? > > > > How will we ensure that core changes don't break any hooks/operators? > > > > How do we support the logging backends for s3/azure/gcp? > > > > What would the release process be for the "sub"-packages? > > > > There is nothing stopping someone /currently/ creating their own > > operators package. There is nothing what-so-ever special about the > > |airflow.operators| package namespace, and for example Google could > > choose to release a airflow-gcp-operators package now and tell people to > > |from gcp.airflow.operators import SomeNewOperator|. > > > > My view on this currently is -1 as I don't see it solving any problem > > than test speed (which is a big one, yes) but doesn't reduce the amount > > of workload on the committers - rather it increases it by having a more > > complex release process (each sub-project would still have to follow the > > normal Apache voting process) and having 24 repos to check for PRs > > rather than just 1. > > > > Am I missing something? > > > > ("Core" vs "contrib" made sense when Airflow was still under Airbnb, we > > should probably just move everything from contrib out to core pre 2.0.0) > > > > -ash > > > > airflowuser wrote on 08/01/2019 15:44: > > > I think the operator should be placed by the source. > > > If it's MySQLToHiveOperator then it would be placed in MySQL package. > > > > > > > > > The BIG question here is if this serve actual improvement like faster > > deployment of hook/operators bug-fix to Airflow users (faster than actual > > Airflow release) or this is mere cosmetic issue. > > > > > > I assume that this also covers the unnecessary separation of core and > > contrib. > > > > > > > > > > > > Sent with ProtonMail Secure Email. > > > > > > ‐‐‐‐‐‐‐ Original Message ‐‐‐‐‐‐‐ > > > On Monday, January 7, 2019 10:16 PM, Maxime Beauchemin < > > maximebeauche...@gmail.com> wrote: > > > > > >> Something to think about is how data transfer operators like the > > >> MysqlToHiveOperator usually rely on 2 hooks. With a package-specific > > >> approach that may mean something like an `airflow-hive`, > `airflow-mysql` > > >> and `airflow-mysql-hive` packages, where the `airflow-mysql-hive` > > package > > >> depends on the two other packages. > > >> > > >> It's just a matter of having a clear strategy, good naming conventions > > and > > >> a nice central place in the docs that centralize a list of approved > > >> packages. > > >> > > >> Max > > >> > > >> On Mon, Jan 7, 2019 at 9:05 AM Tim Swast sw...@google.com.invalid > > wrote: > > >> > > >>> I've created AIP-8: > > >>> > > > https://cwiki.apache.org/confluence/pages/viewpage.action?pageId=100827303 > > >>> To follow-up from the discussion about splitting hooks/operators out > > of the > > >>> core Airflow package at > > >>> http://mail-archives.apache.org/mod_mbox/airflow-dev/201809.mbox/< > > 308670db-bd2a-4738-81b1-3f6fb312c...@apache.org> > > >>> I propose packaging based on the target system, informed by the > > existing > > >>> hooks in both core and contrib. This will allow those with the > relevant > > >>> expertise in each target system to respond to contributions / issues > > >>> without having to follow the flood of everything Airflow-related. It > > will > > >>> also decrease the surface area of the core package, helping with > > >>> testability and long-term maintenance. > > >>> > > >>> - • *Tim Swast > > >>> - • *Software Friendliness Engineer > > >>> - • *Google Cloud Developer Relations > > >>> - • *Seattle, WA, USA > > > > > > > > -- Jarek Potiuk Polidea <https://www.polidea.com/> | Principal Software Engineer M: +48 660 796 129 <+48660796129> E: jarek.pot...@polidea.com
