DMTN-112: LSST DM Vault

• Adam Thornton and
• Russ Allbery

Latest Revision: 2020-05-19

1   Location and Basic Usage

LSST Data Management maintains an instance of HashiCorp’s Vault product at vault.lsst.codes. To use Vault, set VAULT_ADDR to https://vault.lsst.codes, and set the appropriate token (described later) in the environment variable VAULT_TOKEN. Then use the Vault CLI (or other client of your choice) to access secrets under the structure allowed for your token.

Note that we are using Version 2 of the KV Secret Engine (allowing versioned secrets), and therefore you must read and write secrets with vault kv get or vault kv put rather than simple vault read or vault write commands.

2   Vault Implementation

There is currently a single Vault instance for LSST Data Management. That instance is deployed in the Roundtable Kubernetes cluster hosted on GCP. It is deployed using the standard HashiCorp Vault Helm chart. The server uses Let’s Encrypt certificates and does not require client certificate authentication. See the operational documentation for more information.

Figure 1 Roundtable Vault deployment

In the future, we may separate the Vault instance for production services running at the LDF from the Roundtable Vault for other supporting services and test environments.

Each Kubernetes cluster that uses Vault to store secrets has one instance of the Kubernetes Vault Secrets Operator deployed in the cluster. This service is responsible for retrieving secrets from Vault and materializing them as Kubernetes Secret resources. This is configured via Kubernetes VaultSecret resources.

HashiCorp provides a Vault Agent Injector as an alternate way to integrate Kubernetes workloads with Vault. We considered using this instead of Vault Secrets Operator primarily because HashiCorp supports it, but decided against it for several reasons:

1. Vault Secrets Operator allows us to generate one Vault token per Kubernetes cluster that has read access to all secrets for that cluster. Vault Agent Injector requires either configuring tokens per service or requires configuring Kubernetes or GCP authentication to Vault, both of which are more complex.
2. Vault Secrets Operator exposes the secrets as Kubernetes secrets, which allows for easy interoperability with Helm charts and other resources that expect Kubernetes secrets. Vault Agent Injector creates a separate local file system, which applications then have to be configured to use.
3. Injecting sidecars can cause problems and complexity with some Kubernetes workloads that don’t interact well with sidecar processes.

3   Taxonomy

There are two major use cases for employing Vault.

The primary, and preferred, use case is in conjunction with the Kubernetes Vault Secrets Operator. If that is the use case, the secret paths should be organized as:

secret/k8s_operator/:k8s_cluster_fqdn:

An example thereof would be secret/k8s_operator/lsst-lsp-stable.ncsa.illinois.edu. In this case, the owner of the relevant Kubernetes cluster may choose how to organize secrets under that path. We recommend using a structure like:

secret/k8s_operator/:k8s_cluster_fqdn:/:application:

For example, the secret for a SQuaRE microservice named uservice-ghslacker deployed to Roundtable would be named secret/k8s_operator/roundtable.lsst.codes/uservice-ghslacker. If the application required more than one secret, that would instead be a folder containing multiple secrets.

The second use case is as a generic secret store.

In that case, our intention is for Vault to be organized with secret paths under the top-level secret store (secret/) as follows:

secret/:subsystem:/:team:/:category:/:instance:

For instance:

secret/dm/square/credentials/github.com

The Vault Secrets Operator use case is greatly preferred.

4   Tokens

Each secret path will have two tokens created: read and write. The read token can view but not alter data, while the write token can create, update, or delete data within the secret path.

An installation of the Kubernetes Vault Secrets Operator will be given a read token for the entire secret/k8s_operator/:k8s_cluster_fqdn: path for that Kubernetes cluster. (In the future, we may replace this with Kubernetes authentication for the case of a Vault Secrets Operator running in the same cluster as Vault itself.)

5   Token Acquisition and Revocation

To acquire a token pair, ask Russ Allbery (or any other SQuaRE team member) to create a pair for your desired secret path. Assuming that the path is correctly-structured, he will give you a pair of tokens (both id and accessor) for reading and writing to the secret path.

To revoke or renew these tokens, indicate to Russ (or another SQuaRE team member) what path you want revoked or renewed, and (if revocation) whether the corresponding data should be deleted as well.

6   Administrative Tools

Administrative tools for working with Vault can be found at the LSST Vault Utils GitHub Repository or by pip-installing lsstvaultutils.

Without an administrative token (limited to SQuaRE team members), you will not be able to use the tokenadmin tool, which is the tool by which token issuance and revocation is managed.

With multiple write tokens for different paths, you can use the multisecret tool to add a secret to the same relative path across multiple vault secrets paths.

With a write token you will also be able to use vaultrmrf, which is exactly as dangerous as it sounds.