pulumi-hugo-cn/themes/default/content/learn/building-with-pulumi/stack-references/index.md

---
title_tag: Understanding Stack References | Learn Pulumi
title: "Understanding Stack References"
layout: topic
date: 2021-09-20T08:33:49-05:00
draft: false
description: Learn how to share outputs across stacks with stack references.
meta_desc: Learn what stack references are, how they differ from stack outputs, and how to share stack outputs from one Pulumi program to another in this tutorial.
index: 3
estimated_time: 10
meta_image: meta.png
authors:
    - matt-stratton
tags:
    - stacks
    - outputs
---

We've created some resources. Now, let's see how we can use outputs outside of
Pulumi. In this part, we're going to explore more about stacks, _stack outputs_,
and _stack references_. Stack outputs are, as you might guess, the values
exported from any given stack. These values can also be obtained from the
[Pulumi Service](https://app.pulumi.com), and they're extremely useful when you
want to run commands with the CLI that reference those values. Note, though,
that stack outputs are for the current stack only. If you want to get values
from another stack, you want to use stack references, which bridge different
stacks through inter-stack dependencies.

Stack references allow you to access the outputs of one stack from another
stack. Inter-stack dependencies allow one stack to reference the outputs of
another stack.

For this section, we are going to create a new Pulumi program that will bring in
the stack outputs from the program we just created.

Let's start by making our new Pulumi program in a new directory:

{{< chooser language "typescript,python,go,yaml" / >}}

{{% choosable language typescript %}}

```bash
$ mkdir my-second-app
$ cd my-second-app
$ pulumi new typescript -y
```

{{% /choosable %}}

{{% choosable language python %}}

```bash
$ mkdir my-second-app
$ cd my-second-app
$ pulumi new python -y
```

{{% /choosable %}}

{{% choosable language go %}}

```bash
$ mkdir my-second-app
$ cd my-second-app
$ pulumi new go -y
```

{{% /choosable %}}

{{% choosable language yaml %}}

```bash
$ mkdir my-second-app
$ cd my-second-app
$ pulumi new yaml -y
```

{{% /choosable %}}

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

```bash
$ 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 {{< langfile >}} file inside of `my-second-app`.

{{< chooser language "typescript,python,go,yaml" / >}}

{{% choosable language typescript %}}

```typescript
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.

{{% /choosable %}}

{{% choosable language python %}}

```python
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.

{{% /choosable %}}

{{% choosable language go %}}

```go
package main

import (
	"fmt"

	"github.com/pulumi/pulumi/sdk/v3/go/pulumi"
	"github.com/pulumi/pulumi/sdk/v3/go/pulumi/config"
)

func main() {
	pulumi.Run(func(ctx *pulumi.Context) error {
		cfg := config.New(ctx, "")
		stack := ctx.Stack()
		org := cfg.Require("org")

		stackRef, err := pulumi.NewStackReference(ctx, fmt.Sprintf("%v/my-first-app/%v", org, stack), nil)
		if err != nil {
			return err
		}

		ctx.Export("shopUrl", stackRef.GetOutput(pulumi.String("url")))
		return nil
	})
}
```

You'll also need to run `go mod tidy` in the `my-second-app` directory.

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.

{{% /choosable %}}

{{% choosable language yaml %}}

```yaml
name: my-second-app
runtime: yaml
description: A minimal Pulumi YAML program

config:
  org: string

variables:
  firstStackName: ${org}/my-first-app/${pulumi.stack}

resources:
  stackRef:
    type: pulumi:pulumi:StackReference
    properties:
      name: ${firstStackName}

outputs:
  shopUrl: ${stackRef.outputs["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 `pulumi.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.

{{% /choosable %}}

Set the `org` configuration variable using `pulumi config set`:

```bash
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:

```bash

     Type                 Name               Status
     pulumi:pulumi:Stack  my-second-app-staging

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

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 staged API to the staged frontend application to see how they might
work together.

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