Understand stacks

Learning how to switch the infrastructure backend of your code.

In the previous section, you might have already noticed the term stack in the logs and on the dashboard.

Stacks

A stack is the combination of tools and infrastructure that your pipelines can run on. When you run ZenML code without configuring a stack, the pipeline will run on the so-called default stack.

Separation of code from configuration and infrastructure

As visualized in the diagram above, there are two separate domains that are connected through ZenML. The left side shows the code domain. The user's Python code is translated into a ZenML pipeline. On the right side, you can see the infrastructure domain, in this case, an instance of the default stack. By separating these two domains, it is easy to switch the environment that the pipeline runs on without making any changes in the code. It also allows domain experts to write code/configure infrastructure without worrying about the other domain.

The `default` stack

You can explore all your stacks in the dashboard. When you click on a specific one you can see its configuration and all the pipeline runs that were executed using this stack.

zenml stack describe lets you find out details about your active stack:

...
        Stack Configuration        
┏━━━━━━━━━━━━━━━━┯━━━━━━━━━━━━━━━━┓
┃ COMPONENT_TYPE │ COMPONENT_NAME ┃
┠────────────────┼────────────────┨
┃ ARTIFACT_STORE │ default        ┃
┠────────────────┼────────────────┨
┃ ORCHESTRATOR   │ default        ┃
┗━━━━━━━━━━━━━━━━┷━━━━━━━━━━━━━━━━┛
     'default' stack (ACTIVE)      
Stack 'default' with id '...' is owned by user default and is 'private'.
...

zenml stack list lets you see all stacks that are registered in your zenml deployment.

...
┏━━━━━━━━┯━━━━━━━━━━━━┯━━━━━━━━━━━┯━━━━━━━━┯━━━━━━━━━┯━━━━━━━━━━━━━━━━┯━━━━━━━━━━━━━━┓
┃ ACTIVE │ STACK NAME │ STACK ID  │ SHARED │ OWNER   │ ARTIFACT_STORE │ ORCHESTRATOR ┃
┠────────┼────────────┼───────────┼────────┼─────────┼────────────────┼──────────────┨
┃   👉   │ default    │ ...       │ ➖     │ default │ default        │ default      ┃
┗━━━━━━━━┷━━━━━━━━━━━━┷━━━━━━━━━━━┷━━━━━━━━┷━━━━━━━━━┷━━━━━━━━━━━━━━━━┷━━━━━━━━━━━━━━┛
...

As you can see a stack can be active on your client. This simply means that any pipeline you run will be using the active stack as its environment.

Components of a stack

As you can see in the section above, a stack consists of multiple components. All stacks have at minimum an orchestrator and an artifact store.

Orchestrator

The orchestrator is responsible for executing the pipeline code. In the simplest case, this will be a simple Python thread on your machine. Let's explore this default orchestrator.

zenml orchestrator list lets you see all orchestrators that are registered in your zenml deployment.

┏━━━━━━━━┯━━━━━━━━━┯━━━━━━━━━━━━━━┯━━━━━━━━┯━━━━━━━━┯━━━━━━━━━┓
┃ ACTIVE │ NAME    │ COMPONENT ID │ FLAVOR │ SHARED │ OWNER   ┃
┠────────┼─────────┼──────────────┼────────┼────────┼─────────┨
┃   👉   │ default │ ...          │ local  │ ➖     │ default ┃
┗━━━━━━━━┷━━━━━━━━━┷━━━━━━━━━━━━━━┷━━━━━━━━┷━━━━━━━━┷━━━━━━━━━┛

Artifact store

The artifact store is responsible for persisting the step outputs. As we learned in the previous section, the step outputs are not passed along in memory, rather the outputs of each step are stored in the artifact store and then loaded from there when the next step needs them. By default this will also be on your own machine:

zenml artifact-store list lets you see all artifact stores that are registered in your zenml deployment.

┏━━━━━━━━┯━━━━━━━━━┯━━━━━━━━━━━━━━┯━━━━━━━━┯━━━━━━━━┯━━━━━━━━━┓
┃ ACTIVE │ NAME    │ COMPONENT ID │ FLAVOR │ SHARED │ OWNER   ┃
┠────────┼─────────┼──────────────┼────────┼────────┼─────────┨
┃   👉   │ default │ ...          │ local  │ ➖     │ default ┃
┗━━━━━━━━┷━━━━━━━━━┷━━━━━━━━━━━━━━┷━━━━━━━━┷━━━━━━━━┷━━━━━━━━━┛

There are many more components that you can add to your stacks, like experiment trackers, model deployers, and more. You can see all supported stack component types in a single table view here

Registering a stack

Just to illustrate how to interact with stacks, let's create an alternate local stack. We start by first creating a local artifact store.

Create an artifact store

zenml artifact-store register my_artifact_store --flavor=local

Let's understand the individual parts of this command:

artifact-store : This describes the top-level group, to find other stack components simply run zenml --help
register : Here we want to register a new component, instead, we could also update , delete and more zenml artifact-store --help will give you all possibilities
my_artifact_store : This is the unique name that the stack component will have.
--flavor=local: A flavor is a possible implementation for a stack component. So in the case of an artifact store, this could be an s3-bucket or a local filesystem. You can find out all possibilities with zenml artifact-store flavor --list

This will be the output that you can expect from the command above.

Using the default local database.
Running with active workspace: 'default' (global)
Running with active stack: 'default' (global)
Successfully registered artifact_store `my_artifact_store`.bash

To see the new artifact store that you just registered, just run:

zenml artifact-store describe my_artifact_store

Create a local stack

With the artifact store created, we can now create a new stack with this artifact store.

zenml stack register my_stack -o default -a my_artifact_store

stack : This is the CLI group that enables interactions with the stacks
register: Here we want to register a new stack. Explore other operations withzenml stack --help.
my_stack : This is the unique name that the stack will have.
--orchestrator or -o are used to specify which orchestrator to use for the stack
--artifact-store or -a are used to specify which artifact store to use for the stack

The output for the command should look something like this:

Using the default local database.
Running with active workspace: 'default' (repository)
Stack 'my_stack' successfully registered!

You can inspect the stack with the following command:

 zenml stack describe my_stack

Which will give you an output like this:

         Stack Configuration          
┏━━━━━━━━━━━━━━━━┯━━━━━━━━━━━━━━━━━━━┓
┃ COMPONENT_TYPE │ COMPONENT_NAME    ┃
┠────────────────┼───────────────────┨
┃ ORCHESTRATOR   │ default           ┃
┠────────────────┼───────────────────┨
┃ ARTIFACT_STORE │ my_artifact_store ┃
┗━━━━━━━━━━━━━━━━┷━━━━━━━━━━━━━━━━━━━┛
           'my_stack' stack           
Stack 'my_stack' with id '...' is owned by user default and is 'private'.

To run a pipeline using the new stack:

Set the stack as active on your client
```
zenml stack set my_stack
```
Run your pipeline code (you can use the code from this previous section)
```
python run.py
```