Understanding Stack References

Stack references extend the utility of stack outputs by allowing you to access them programmatically from another Pulumi program at runtime.

In this section, you’ll create a new project and stack that’ll use the stack outputs from the program we created in the previous topic.

Let’s start by making a new program in a new directory, alongside my-first-app:

$ mkdir ../my-second-app
$ cd ../my-second-app
$ pulumi new typescript -y

$ mkdir ../my-second-app
$ cd ../my-second-app
$ pulumi new python -y

Let’s go ahead and create a staging stack here as well:

$ pulumi stack init staging

Now comes the fun part! Let’s add a little code to pull in the values from the my-first-app stacks, based on the corresponding environment.

Add this code to the index.js index.ts __main__.py main.go Program.cs Program.fs Program.vb App.java Pulumi.yaml file inside of my-second-app:

import * as pulumi from "@pulumi/pulumi";

const config = new pulumi.Config();
const stack = pulumi.getStack();
const org = config.require("org");

const stackRef = new pulumi.StackReference(`${org}/my-first-app/${stack}`)

export const shopUrl = stackRef.getOutput("url");

The org configuration variable is new, as is the stackRef declaration. That declaration sets up an instance of the StackReference class, which needs the fully qualified name of the stack as an input. Here, org is the organization associated with your account, my-first-app is the name of the project you’ve been working in, and stack is the stack that you want to reference. If you have an individual account, the org is your account name. The export then grabs the url output from the other stack.

import pulumi

config = pulumi.Config()
stack = pulumi.get_stack()
org = config.require("org")

stack_ref = pulumi.StackReference(f"{org}/my-first-app/{stack}")

pulumi.export("shopUrl", stack_ref.get_output("url"))

The org configuration variable is new, as is the stack_ref declaration. That declaration sets up an instance of the StackReference class, which needs the fully qualified name of the stack as an input. Here, org is the organization associated with your account, my-first-app is the name of the project you’ve been working in, and stack is the stack that you want to reference. If you have an individual account, the org is your account name. The export then grabs the url output from the other stack.

Set the org configuration variable using pulumi config set:

pulumi config set org <YOURNAME>

Run pulumi up. You’ll see the value gets exported from the other project’s stack to reference in this new project’s stack:

$ pulumi up
...

Updating (staging)
...

     Type                 Name                   Status
 +   pulumi:pulumi:Stack  my-second-app-staging  created (1s)

Outputs:
    shopUrl: "http://localhost:3002"

Resources:
    + 1 created

Duration: 3s

These exported values are incredibly useful when using Pulumi stacks. For example, let’s say you have two systems that depend on one another, perhaps a frontend application with a database and a complex backend API. You might have two separate staging environments that you want to have reference one another. You can use stack references to share automatically generated connection strings from the staging API to the staging frontend application to see how they might work together.

Next up, we’re going to change gears and start exploring how Pulumi handles secrets.

← Previous: Working with Secrets Back to Building with Pulumi →

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