Managing Secrets with Pulumi

Posted by Matt Ellis
Find me on:

We’ve had a 1st class concept of encrypted secrets configuration ever since first releasing Pulumi. Customers have told us they love having such a simple and easy way to ensure safe management of tokens, database passwords, and more. Since launching, however, we’ve also heard that you’d like more control over encryption and to see this protection expanded to cover not just configuration, but all of the secret data within their Pulumi deployments.

To support this, we’ve added two new features to Pulumi in our latest 0.17.12 release:

  • Automatic tracking of secret values throughout a Pulumi program to ensure that all such values are always encrypted in the resulting state, no matter how they are used.
  • A new option to use custom client-side encryption, instead of the default of using the Pulumi backend for encryption, to have full control over the secrets encryption and decryption.

Together, these features provide you with complete control over how secrets are managed within Pulumi deployments. We have worked with customers with advanced security and compliance needs while developing this feature, enabling them to use our online hosted SaaS with even greater confidence.

Secrets and State

Like many infrastructure as code systems, Pulumi uses a state file to describe the current state of your infrastructure. When you run pulumi up, Pulumi takes your existing state file, runs your program to compute a new desired state and compares the two states. It makes updates to the current state so it matches the desired state and updates its state file as it does so. As part of this, Pulumi needs to retain all the input values passed to resources in the state file, so it can detect if they have changed from run to run.

While Pulumi has allowed you to pass --secret to force configuration values to be encrypted before being stored in a stack’s configuration file, if you used these configuration values as inputs to resources, they would be stored in plain text in the state file. While the state file itself is stored securely (we encrypt all state files in transit and at rest), anyone with access to the state file itself would be able to see the plain text for all of these secrets.

By adding first class support for secrets with Pulumi, we are now able to automatically track secrets across your program’s execution and ensure that secret values are encrypted in the state file. This means you can use secrets confidently without worrying about accidentally leaking plain text values. Let’s take a look at how it works!

Output and Secrets

To start, let’s talk a bit about Output, one of the centerpieces of the Pulumi programming model. Output<T> ties together a value (which may not be ready yet, since it could depend on some data from a cloud resource that is still being created) and resources that the output depends on. When you create a resource with Pulumi, the properties of that resource are Output's that you can pass to other resources. Pulumi uses the information tracked by Output to understand dependencies between different resources. For example when an Output<string> is used to construct a resource, Pulumi knows this resource depends on any resources that were used to generate that output. The underlying value that the Output wraps is what we store in the state file as an input for this new resource.

With 0.17.11 of Pulumi, we now have Output<T> track if it contains secret data. If it does, we ensure that the data is encrypted before we store it in the state file. There are few ways to create secret Outputs today:

By fetching values from the Config object in the JavaScript and Python SDKs, using the newly added getSecret or requireSecret (JavaScript) and get_secret or require_secret (Python), as well as some type specific overloads. These methods fetch the requested value from the configuration bag and then wrap it up in an Output which is marked as a secret.
By using pulumi.secret (JavaScript) or pulumi.Output.secret (Python) to take an existing value and wrap it up in an Output which is marked as a secret. These behave the same way as pulumi.output (JavaScript) and pulumi.Output.from_input (Python) except they also mark the returned output as a secret.
By retrieving an output that is marked as a secret from a resource.

When constructing a resource that has one or more secret inputs for a property, the entire corresponding output property of the resource is marked as a secret as well. In addition, as you combine outputs together, via all or apply, the resulting output is marked as a secret if any of the inputs values where themselves secrets. This means that just like dependency information, the “secret-ness” of an output flow naturally as you combine it with other data.

Let’s take a look at a small program which creates an AWS Systems Manager parameter, based on a secret configuration value.

Here’s the program we’ll be using:

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

const cfg = new pulumi.Config();
const secretMessage = cfg.requireSecret("secretMessage");

const param = new aws.ssm.Parameter("secretParameter", {
    type: "SecureString",
    value: secretMessage.apply(s => s.toUpperCase())
});

export const paramId = param.id;
export const paramValue = param.value;

In the above code sample, we’re using the new requireSecret method to pull out a configuration value as a secret. In addition, we use an apply to transform the string to all uppercase before creating our SSM Parameter. Because secretMessage was marked as a secret, this new value is also marked as a secret. It’s important to note the function that runs during the apply has access to the unencrypted value, so you need to be sure that your code inside the apply does not cause the secret to leak (for example, don’t write it to a text file!)

For a demo, let’s create a new stack, target us-west-2 in AWS and set a secret message:

$ pulumi stack init dev
$ pulumi config set aws:region us-west-2
$ pulumi config set --secret secretMessage "it's a secret to everybody"

Now, when we run pulumi up after creating a new stack, we’ll see the following preview:

Previewing update (dev):

     Type                  Name              Plan       
 +   pulumi:pulumi:Stack   secrets-blog-dev  create     
 +   └─ aws:ssm:Parameter  secretParameter   create     
 
Resources:
    + 2 to create

If we look at the details for this deployment (before actually running the update), we can see that the value of this resource has been marked as a secret:

+ pulumi:pulumi:Stack: (create)
    [urn=urn:pulumi:dev::secrets-blog::pulumi:pulumi:Stack::secrets-blog-dev]
    + aws:ssm/parameter:Parameter: (create)
        [urn=urn:pulumi:dev::secrets-blog::aws:ssm/parameter:Parameter::secretParameter]
        name      : "secretParameter-1d79dca"
        type      : "SecureString"
        value     : "[secret]"

Once we’ve deployed our program, we can use pulumi stack export to look at the state file for our deployment, we see that the value is encrypted there as well (I’ve removed some uninteresting fields here, for clarity):

{
    "urn": "urn:pulumi:dev::secrets-blog::aws:ssm/parameter:Parameter::secretParameter",
    ...snip...
    "inputs": {
        ...snip...
        "name": "secretParameter-56f0ffb",
        "type": "SecureString",
        "value": {
            "4dabf18193072939515e22adb298388d": "1b47061264138c4ac30d75fd1eb44270",
            "ciphertext": "AAABAMo1ZLFpKzoHxUkGPXsUMjLBANri5fkPiveYUrjuMzsqONi2U1LnZSPxsN1vvFTs50skEru+Ff6N"
        }
    },
    "outputs": {
        ...snip...
        "name": "secretParameter-56f0ffb",
        "type": "SecureString",
        "value": {
            "4dabf18193072939515e22adb298388d": "1b47061264138c4ac30d75fd1eb44270",
            "ciphertext": "AAABAOjpCFOLHMzP4G9OXc4r+mQs6/4DJv2aWO+vX0LyYHLjfawAHWFlRmv3dErda6Ip48pRB19bBL9t"
        }
    }
    ...snip...
}

As you can see, the value is encrypted in the state file for this resource! Also note that because the value was marked as a secret input, the corresponding copy in the output section of the state file was also marked as a secret. Pulumi ensures that any outputs with the same names as inputs which had secret data are also considered secrets. If there are additional outputs you want to set as secrets, you can pass the additionalSecretOutputs (JavaScript) or additional_secret_outputs (Python) resource option when constructing a resource to provide a list of other property names you want treated as secrets including computed output properties of a resource which might be sensitive, like generated passwords or access credentials.

Configuring your secrets provider

You might be wondering how these values are actually encrypted. We use the same encryption that we have always used for our configuration system. This means when storing state with pulumi.com, we use a key managed by the pulumi.com service, specific to your stack, to encrypt everything. Some users have asked for more control over what key is used (and the ability to use a key not managed by Pulumi at all!)

When creating a new stack (via pulumi stack init or pulumi new), you may now pass --secrets-provider passphrase to specify that both configuration secrets and secrets stored in the state file should be encrypted using a key derived from a passphrase (if you’ve used Pulumi’s local state storage mode, this will be familiar to you). When you use a passphrase, we use PBKDF2 to derive a 32 byte encryption key, which we then use with the AES-256-GCM encryption algorithm to encrypt your value (using a random 12 byte nonce per value encrypted). Let’s run through deploying the same code but using the passphrase secret provider:

First, I create a new stack, setting the secrets provider to passphrase:

$ pulumi stack init dev --secrets-provider passphrase
Enter your passphrase to protect config/secrets:
Re-enter your passphrase to confirm:
Created stack 'dev'

As part of creating the stack, I had to enter a passphrase, which I’ll have to use during future updates. This passphrase is used to derive the key used for both configuration and state management. I can now configure my stack as I please:

$ pulumi config set aws:region us-west-2
$ pulumi config set secretMessage --secret "it's a secret to everybody"
Enter your passphrase to unlock config/secrets
    (set PULUMI_CONFIG_PASSPHRASE to remember):

Note that to set the secret value, I had to provide my passphrase (since it is needed to generate the key that is used to encrypt the value).

Finally, I can run pulumi up, here I’m prompted to enter my passphrase again. I could also set PULUMI_CONFIG_PASSPHRASE in my environment. You might do this locally as part of your local development loop (so you don’t have to type your passphrase over and over) or in your CI system (where you’d be unable to type your passphrase in interactively).

$ pulumi up
Enter your passphrase to unlock config/secrets
    (set PULUMI_CONFIG_PASSPHRASE to remember):

If we use pulumi stack export again to examine the state file, we can see that the structure of the ciphertext has changed:

"value": {
    "4dabf18193072939515e22adb298388d": "1b47061264138c4ac30d75fd1eb44270",
    "ciphertext": "v1:qdfpSdF8vCWRJIDa:4gPQAMRSXi+5ap0koiZBsSVRnqzbp79cSEyWnLYkD9M5S/oI8qhgy521IBA="
}

The change is because we are no longer using the Pulumi service to encrypt or decrypt this data, instead the encryption and decryption happens locally, the data never leaves your machine. So while I get to continue to use pulumi.com to store state for my stack, I don’t have to worry about my secrets being encrypted with a key managed by a third party.

Support for changing the secrets provider for an existing stack is on its way. To track progress on this feature, please see GitHub issue #481.

What’s Next

In addition to passphrase based encryption, we plan to add support for encrypting using AWS KMS, Azure KeyVault and GCP KMS in the coming weeks.

The whole team is super excited about this feature and we love how nicely we were able to integrate it into our overall programming model. With these two new features, Pulumi users gain full control over how their secrets are managed, but without sacrificing usability and productivity. We’re excited for you all to start playing around with it! Pulumi is open source, free to use, and works today with variety of clouds - check it out.

Topics: Features, Security

Posted on May 17, 2019 2:30:15 PM