@Marvin when I work on a flow locally, in development, I want to write files to my local file system. When I deploy that flow, for production, I want files to be written in S3. What is the recommended pattern to easily switch from local to remote file system, depending on the context?

The recommended pattern for handling situations where you want to switch between local and remote file systems is to use Prefect's block system. Blocks in Prefect can be defined for different environments, allowing you to swap configurations at runtime. For example, you can define a block for your development environment that writes to the local file system and another block for your production environment that writes to an S3 bucket. To switch between local and remote filesystems, you would typically have a block that represents each filesystem. During development, you would load and use the block that points to the local file system. When deploying to production, you would load the block that is configured to write to S3. Here's a simplified example of how you might set up blocks for filesystems in Prefect: 1. Define blocks for each environment: - A block for a local filesystem (for development). - A block for an S3 bucket (for production). 2. Depending on the context (development or production), you would load the appropriate block using Prefect's block storage system, which allows you to access and use different configuration setups: - In your development flow, you might have

FileSystemLocal.load("dev")

to load the configuration for your local filesystem. - In your production flow, you might use

FileSystemS3.load("prod")

to load the configuration for S3. By using blocks implemented with interfaces, Prefect allows you to easily swap out components without needing to change the flow's logic. This pattern of using blocks and loading the appropriate configuration at runtime makes it easy to have flexible and environment-specific handling of different filesystems. For more detailed guidance, I would recommend reviewing Prefect's documentation regarding blocks or looking at examples within the community that demonstrate this setup.

@Marvin When you say "depending on the context", what evaluates the context? Should I have a if condition in the code? Is it based on a tag? On a command when running the flow?

To evaluate the context in which your Prefect flow runs, especially when switching between different environments such as development and production, you typically use one of the following methods: 1. Environment Variables: You can use environment variables to differentiate between environments. When the flow runs, it checks specified environment variables to determine which file system to use. This is common in cloud-native applications and is useful when deploying flows with Prefect Cloud or Server. You reference environment variables with the syntax

{{ $MY_ENV_VAR }}

in your Prefect flow to make decisions based on their values at runtime. 2. Prefect Profiles and Configuration: Prefect allows you to use profiles to manage different settings configurations. By using the Prefect CLI, you can set up various configuration profiles and then use the

--profile

option when running your flow. An example command might be

prefect --profile "prod" run flow...

, which will use the settings associated with the "prod" profile. 3. Conditional Logic (if statement): Inside your flow code, you might use an

if

condition to check a variable or state that indicates the current environment. This variable could be set manually, derived from environment variables, or based on other runtime parameters. 4. Prefect Variables: Prefect variables, which are referenced through the syntax

{{ prefect.variables.variable_name }}

, can be used to store non-sensitive, reusable pieces of information that might vary between different environments or runtime contexts. So, the context could be evaluated using one or a combination of these approaches: - An

if

statement that checks environment variables or Prefect variables. - Command-line arguments, such as a profile flag when running the flow. - Environment variables that are fetched within the flow to determine the runtime environment. Which method—or combination of methods—you use will depend on your particular setup, your deployment processes, and what works best for your workflow. The key is that Prefect offers flexible ways to handle environment-specific logic, enabling you to switch between environments without modifying the core logic of your flows.