Pentagon is a small application designed to run as a Kubernetes CronJob to periodically copy secrets stored in Vault into equivalent Kubernetes Secrets, keeping them synchronized. Naturally, this should be used with care as "standard" Kubernetes Secrets are simply obfuscated as base64-encoded strings. However, one can and should use more secure methods of securing secrets including Google's KMS and restricting roles and service accounts appropriately.
Use at your own risk...
That's a good question. If you have a highly-available Vault setup that is stable and performant and you're able to modify your applications to query Vault, that's a completely reasonable approach to take. If you don't have such a setup, Pentagon provides a way to cache things securely in Kubernetes secrets which can then be provided to applications without directly introducing a Vault dependency.
Pentagon requires a simple YAML configuration file, the path to which should be passed as the first and only argument to the application. It is recommended that you store this configuration in a ConfigMap and reference it in the CronJob specification. A sample configuration follows:
vault:
url: <url to vault>
authType: # "token" or "gcp-default"
token: <token value> # if authType == "token" is provided
defaultEngineType: # "kv" or "kv-v2" (currently supported)
role: "vault role" # if left empty, queries the GCP metadata service
tls: # optional [tls options](https://godoc.org/github.com/hashicorp/vault/api#TLSConfig)
namespace: <kubernetes namespace for created secrets>
label: <label value to set for the 'pentagon'-created secrets>
mappings:
# mappings from vault paths to kubernetes secret names
- vaultPath: secret/data/vault-path
secretName: k8s-secretname
vaultEngineType: # optionally "kv" or "kv-v2" to override the defaultEngineType specified above
secretType: Opaque # optionally - default "Opaque" e.g.: "kubernetes.io/tls"By default, Pentagon will add a metadata label with the key pentagon and the value default. At the least, this helps identify Pentagon as the creator and maintainer of the secret.
If you set the label configuration parameter, you can control the value of the label, allowing multiple Pentagon instances to exist without stepping on each other. Setting a non-default label also enables reconciliation which will cleanup any secrets that were created by Pentagon with a matching label, but are no longer present in the mappings configuration. This provides a simple way to ensure that old secret data does not remain present in your system after its time has passed.
Apparently, different Vault secrets engines have slightly different APIs for returning data. For instance, here is the response for version 1 of the key/value store:
{
"request_id": "12a0c057-f475-4bbd-6305-e4c07e66805c",
"lease_id": "",
"renewable": false,
"lease_duration": 2764800,
"data": {
"foo": "world"
},
"wrap_info": null,
"warnings": null,
"auth": null
}Notice that the data object has the foo key embedded directly. Alternatively, here is the response for version 2 of the key/value store:
{
"request_id": "78b921ae-79a8-d7e3-da16-336b634fff22",
"lease_id": "",
"renewable": false,
"lease_duration": 0,
"data": {
"data": {
"foo": "world"
},
"metadata": {
"created_time": "2019-10-01T19:36:25.285387Z",
"deletion_time": "",
"destroyed": false,
"version": 1
}
},
"wrap_info": null,
"warnings": null,
"auth": null
}Notice the extra data element nested inside the outer data. Vault secrets engines can be mounted at arbitrary paths and it does not appear to be possible to reliably detect which engine was used in the API response directly. In order to properly unwrap the secret data,indicate either kv or kv-v2 as the vaultEngineType in the configuration. In the common case of using only one secrets engine, simply define the defaultEngineType in the vault configuration block and the mapping-level vaultEngineType will inherit the default. For compatibility, the unset default value defaults to kv. Note that this differs from the current default that Vault itself uses for the key/value secrets engine.
The application will return 0 on success (when all keys were copied/updated successfully). A complete list of all possible return values follows:
| Return Value | Description |
|---|---|
| 0 | Successfully copied all keys. |
| 10 | Incorrect number of arguments. |
| 20 | Error opening configuration file. |
| 21 | Error parsing YAML configuration file. |
| 22 | Configuration error. |
| 30 | Unable to instantiate vault client. |
| 31 | Unable to instantiate kubernetes client. |
| 40 | Error copying keys. |
Pentagon is intended to be run as a cron job to periodically sync keys. In order to create/update Kubernetes secrets extra permissions are required. It is recommended to grant those extra permissions to a separate service account which the application will also use. The following roles is a sample configuration:
apiVersion: batch/v1beta1
kind: CronJob
metadata:
name: pentagon
spec:
schedule: "0 15 * * *"
concurrencyPolicy: Replace
jobTemplate:
metadata:
labels:
app: pentagon
spec:
parallelism: 1
completions: 1
template:
spec:
serviceAccountName: pentagon # run with a service account that has access to create/update secrets
terminationGracePeriodSeconds: 10
restartPolicy: OnFailure
containers:
- name: pentagon
image: vimeo/pentagon:v1.1.0
args: ["/etc/pentagon/pentagon.yaml"]
imagePullPolicy: Always
resources:
limits:
cpu: 250m
memory: 128Mi
requests:
cpu: 250m
memory: 128Mi
volumeMounts:
- name: pentagon-config
mountPath: /etc/pentagon
readOnly: true
volumes:
- name: pentagon-config
configMap:
name: pentagon-config
---
apiVersion: v1
kind: ConfigMap
metadata:
name: pentagon-config
data:
pentagon.yaml: |
vault:
url: https://vault.address
authType: gcp-default
tls: # optional if you have custom requirements
capath: /etc/cas/custom-root-ca.crt
label: mapped
mappings:
- vaultPath: secret/config/main/foo.key
secretName: foo-key
- vaultPath: secret/ssl/tls/domain.com
secretName: domain.com
secretType: "kubernetes.io/tls"
---
apiVersion: rbac.authorization.k8s.io/v1beta1
kind: Role
metadata:
name: pentagon
rules:
- apiGroups: ["*"]
resources:
- secrets
verbs: ["get", "list", "create", "update", "delete"]
---
apiVersion: v1
kind: ServiceAccount
metadata:
name: pentagon
---
apiVersion: rbac.authorization.k8s.io/v1beta1
kind: RoleBinding
metadata:
name: pentagon
roleRef:
apiGroup: rbac.authorization.k8s.io
kind: Role
name: pentagon
subjects:
- kind: ServiceAccount
name: pentagonPentagon is a production of Vimeo's Core Services team with lots of support from Vimeo SRE.