5 ms·

Is it declarative? Obviously python isn't, but since it's not executed as a script but rather the module passed to pyinfra, it could be, and looks like maybe it

by OJFord 3y ago

Is it declarative? Obviously python isn't, but since it's not executed as a script but rather the module passed to pyinfra, it could be, and looks like maybe it is just registering work to (potentially) do on module load? If so, nice, shout about it more - it's my number one requirement of such a tool, why I think Terraform (or OpenTofu) is great and mostly everything else sucks, and I think it should be everyone's. It's just obviously (at least, once someone makes it available!) the correct paradigm for managing stateful resources and coping with drift.

Fizzadar 3y ago
Yes... and no. It depends on the operation (the docs explicitly state if an operation is _not_ idempotent "stateless operation"). Operations are either: - state definitions, "ensure this apt package is installed" (apt.packages: https://docs.pyinfra.com/en/next/operations/apt.html#operations-apt-packages https://docs.pyinfra.com/en/next/operations/apt.html#operati...) - stateless, "run these shell commands" (server.shell: https://docs.pyinfra.com/en/next/operations/server.html#operations-server-shell https://docs.pyinfra.com/en/next/operations/server.html#oper...) Most operations are state definitions and much preferred, the stateless ones exist to satisfy edge cases where either the state-ful version isn't implemented or simply isn't possible.
- tetha 3y ago
  Ah, so this is similar to the Terraform CDK approach? In Terraform CDK, you use a language like python to compute the set of resources and such you want to have, and then hand that over to the terraform core, which does the usual terraform song and dance to make it happen. This is actually interesting to me, because we struggle with even the simplest data transformations in ansible so much. Like, as soon as you start thinking about doing a simple list comprehension in python in jinja templating, lots and lots of pain starts. From there, we're really starting to think about templating the inventories in some way because it would be less painful.
  - Fizzadar 3y ago
    Interesting, not heard of CDK before! Kind of similar? As long as the language is Python I suppose! Would be possible to integrate with other languages too I guess, not something I’ve ever looked into though. Totally agree on templating which is why inventories have always been python code just as operations, giving maximum flexibility (with some complexity/type confusion drawbacks).
    - F-Lexx 3y ago
      Relevant XKCD: https://xkcd.com/303/ https://xkcd.com/303/
    - 4m1rk 3y ago
      CDK just generates AWS CloudFormation files (There is CDK for TF as well as said before, but is not the AWS official implementation). It's like having a few constructs to allow you generate a YAML or JSON file.
peteradio 3y ago
I never understood the desire to make things declarative. It seemed to me to always hide what is actually happening and it made it more difficult to understand. Is there a simple way to understand why declarative stuff is desirable to some people?
- michaelmior 3y ago
  I think the main reason people like the declarative approach is that done right, it's idempotent. You also don't have to think about the current state of the system at all. You just need to describe what you want it to look like. Of course in practice it can be more nuanced than that, but thinking declaratively can make things much simpler in some scenarios.
  - Spivak 3y ago
    These aren't as related as you think. Ansible is imperative and idempotent.
    - michaelmior 3y ago
      I didn't intend to suggest that the declarative approach is the only way to achieve idempotency.
    - windexh8er 3y ago
      Ansibles' resources are declarative [0]. What part of Ansible is imperative? https://docs.ansible.com/ansible/latest/reference_appendices/glossary.html#term-Declarative https://docs.ansible.com/ansible/latest/reference_appendices...
      - matrss 3y ago
        Ansible playbooks are usually a list of steps to execute in order (imperative). Those steps may try to present a declarative interface to what they are supposed to do, but many fail to fulfill the definition of "declarative" that you have linked. E.g. with the built-in modules it is impossible to declare a desired set of installed packages, only a set of packages to be installed _in addition to all already installed packages_. This means it is impossible to remove an installed package again by removing it from the declaration, you have to specify a second step (imperative) that explicitly removes the package. This makes it impossible to declare a final state for "installed packages" with ansible.
pid-1 3y ago
> Obviously python isn't Obviously you can create declarative idioms in Python
- OJFord 3y ago
  Sure, if you keep reading I described one that it looked like this might be doing.

by OJFord 3y ago

Fizzadar 3y ago

Yes... and no. It depends on the operation (the docs explicitly state if an operation is _not_ idempotent "stateless operation"). Operations are either: - state definitions, "ensure this apt package is installed" (apt.packages: https://docs.pyinfra.com/en/next/operations/apt.html#operations-apt-packages https://docs.pyinfra.com/en/next/operations/apt.html#operati...) - stateless, "run these shell commands" (server.shell: https://docs.pyinfra.com/en/next/operations/server.html#operations-server-shell https://docs.pyinfra.com/en/next/operations/server.html#oper...) Most operations are state definitions and much preferred, the stateless ones exist to satisfy edge cases where either the state-ful version isn't implemented or simply isn't possible.

tetha 3y ago
Ah, so this is similar to the Terraform CDK approach? In Terraform CDK, you use a language like python to compute the set of resources and such you want to have, and then hand that over to the terraform core, which does the usual terraform song and dance to make it happen. This is actually interesting to me, because we struggle with even the simplest data transformations in ansible so much. Like, as soon as you start thinking about doing a simple list comprehension in python in jinja templating, lots and lots of pain starts. From there, we're really starting to think about templating the inventories in some way because it would be less painful.
- Fizzadar 3y ago
  Interesting, not heard of CDK before! Kind of similar? As long as the language is Python I suppose! Would be possible to integrate with other languages too I guess, not something I’ve ever looked into though. Totally agree on templating which is why inventories have always been python code just as operations, giving maximum flexibility (with some complexity/type confusion drawbacks).
  - F-Lexx 3y ago
    Relevant XKCD: https://xkcd.com/303/ https://xkcd.com/303/
  - 4m1rk 3y ago
    CDK just generates AWS CloudFormation files (There is CDK for TF as well as said before, but is not the AWS official implementation). It's like having a few constructs to allow you generate a YAML or JSON file.

peteradio 3y ago

I never understood the desire to make things declarative. It seemed to me to always hide what is actually happening and it made it more difficult to understand. Is there a simple way to understand why declarative stuff is desirable to some people?

michaelmior 3y ago
I think the main reason people like the declarative approach is that done right, it's idempotent. You also don't have to think about the current state of the system at all. You just need to describe what you want it to look like. Of course in practice it can be more nuanced than that, but thinking declaratively can make things much simpler in some scenarios.
- Spivak 3y ago
  These aren't as related as you think. Ansible is imperative and idempotent.
  - michaelmior 3y ago
    I didn't intend to suggest that the declarative approach is the only way to achieve idempotency.
  - windexh8er 3y ago
    Ansibles' resources are declarative [0]. What part of Ansible is imperative? https://docs.ansible.com/ansible/latest/reference_appendices/glossary.html#term-Declarative https://docs.ansible.com/ansible/latest/reference_appendices...
    - matrss 3y ago
      Ansible playbooks are usually a list of steps to execute in order (imperative). Those steps may try to present a declarative interface to what they are supposed to do, but many fail to fulfill the definition of "declarative" that you have linked. E.g. with the built-in modules it is impossible to declare a desired set of installed packages, only a set of packages to be installed _in addition to all already installed packages_. This means it is impossible to remove an installed package again by removing it from the declaration, you have to specify a second step (imperative) that explicitly removes the package. This makes it impossible to declare a final state for "installed packages" with ansible.

pid-1 3y ago

> Obviously python isn't Obviously you can create declarative idioms in Python

OJFord 3y ago
Sure, if you keep reading I described one that it looked like this might be doing.