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Azure Key Vault Agent for ACS (Kubernetes)

An Azure Key Vault agent container that grabs secrets from Azure Key Vault securely and passes them to other containers in its pod, either by shared volume or Kubernetes secrets objects

How does it work?

The Azure Key Vault agent container does the following -

  • It runs before any other container as an init-container
  • It connects to Azure Key Vault using the cluster's service principle
  • It then grabs the desired secrets and/or certificates from Azure Key Vault and stores them in a shared volume (memory only - tmpfs)
  • If a secret refers to a key that is backing a certificate, both private key, certificate (and optionally CA chain) are exported as pem
  • It terminates and let other containers run
  • Finally, other containers have access to the secrets using a shared volume When creating Kubernetes secrets objects -
  • It connects to Azure Key Vault using the cluster's service principle
  • It then grabs the desired secrets from Azure Key Vault and stores them as Kubernetes secrets objects. These objects are stored unencrypted by default in etcd, and are readable by other pods in the namespace.

Advantages

  • Secrets are stored securely in Azure Key Vault
  • Authentication to Azure Key Vault is done securely without any secrets or config maps being used

Requirements

  • A deployed Azure Key Vault
  • A Kubernetes cluster with a working kubectl
  • The Kubernetes cluster's Service principal is added to the Access policies of the Key Vault

How to use it

  • Config your Azure Key Vault to give your cluster's service principle a "get" permission so it can grab secrets
  • Clone the project to your desired folder
  • Build the agent image using docker
cd <project_root>
docker build . -t <image_tag>
  • Push the agent image to your image repository
docker push <image_tag>

  • Edit examples/acs-keyvault-deployment.yaml file and change -

    • <IMAGE_PATH> - the image you just built earlier.
    • <VAULT_URL> - should be something like: https://<NAME>.vault.azure.net.
    • <SECRET_KEYS> - a list of keys and their versions (optional), represented as a string, formatted like: <secret_name>:<secret_version>;<another_secret>. If a secret is backing a certificate, private key and certificate will be downloaded in PEM format at keys/ and certs/ respectively. for example mysecret:9d90276b377b4d9ea10763c153a2f015;anotherone;
    • <DOWNLOAD_CA_CERTIFICATES> - By default, CA certificates are downloaded in PEM format at ca_certs/<certificate_name>/ca.pem. Setting the environment variable to true or false controls this behavior.
    • <CERTS_KEYS> - a list of certificates and their versions (optional), represented as a string, formatted like: <cert_name>:<cert_version>;<another_cert>. Certificates will be downloaded in PEM format.

  • Create the deployment using

kubectl create -f ./examples/acs-keyvault-deployment.yaml
  • Now connect to any of the deployment pods -
kubectl exec -ti test-keyvault-7d94566cdb-7wmx9 -c test-app /bin/sh

and now just view the secrets with

cat /secrets/secrets/<secret_name>
cat /secrets/certs/<certificate_name>
cat /secrets/keys/<key_name>
cat /secrets/certs_ca/<certificate_name>

How to use it - Kubernetes Secrets

  • Config your Azure Key Vault to give your cluster's service principle a "get" permission so it can grab secrets
  • Ensure that your secret names follow Kubernetes standard - must consist of lower case alphanumeric characters, '-' or '.', and must start and end with an alphanumeric character
  • Clone the project to your desired folder
  • Build the agent image using docker
cd <project_root>
docker build . -t <image_tag>
  • Push the agent image to your image repository
docker push <image_tag>
  • Edit examples/acs-keyvault-cronjob.yaml or examples/acs-keyvault-deployment.yaml file and change the following:
  • If you'd like to get all keys from Key Vault dynamically, make sure to remove the SECRET_KEYS variable entirely.
    • <IMAGE_PATH> - the image you just built earlier.
    • <VAULT_URL> - should be something like: https://<NAME>.vault.azure.net.
    • <CREATE_KUBERNETES_SECRETS> - "true" or "false", whether or not you'd like kubernetes secrets objects created.
    • <SECRETS_NAMESPACE> - a string value if you want to use a namespace other than default.
    • <SECRETS_KEYS> - a list of keys and their versions (optional), represented as a string, formatted like: <secret_name>:<secret_version>;<another_secret>. If a secret is backing a certificate, private key and certificate will be downloaded in PEM format at keys/ and certs/ respectively. for example mysecret:9d90276b377b4d9ea10763c153a2f015;anotherone;
    • <DOWNLOAD_CA_CERTIFICATES> - By default, CA certificates are downloaded in PEM format at ca_certs/<certificate_name>/ca.pem. Setting the environment variable to true or false controls this behavior.
    • <VAULT_BASE_URL> - A string value that is the base url of the keyvault. It should look something like this: https://<NAME>.vault.azure.net.
    • <SECRETS_TYPE> - a string value that determines the type of secret created. For example, 'kubernetes.io/tls', 'Opaque' etc. Default is 'Opaque'.
    • If you like to create secrets of a particular kind (for example for use in DaemonSets), create an environment variable with the name of the secret that you are creating in uppercase appended by _SECRET_TYPE. For example, if the key name in keyvault is mysecret then to create a secret of type MyCustomType, set the environment variable MYSECRET_SECRET_TYPE to MyCustomType. This will be applicable only for that secret name, and overrides any value set for '<SECRETS_TYPE>' key. Default is 'Opaque'.
    • If you'd like to install secrets with key value other than the default secret, then you can do that by creating an environment variable with name _SECRETS_DATA_KEY. For example if you have a secret called DBConnectionString and if you would like to install a secret with key as connectionString and value to be the base64 encoded connection string, then create a environment variable DBCONNECTIONSTRING_SECRETS_DATA_KEY and set its value to connectionString
    • <AUTO_DETECT_AAD_TENANT> - By default, tenantId from cloud config is used for authentication. Setting the environment variable to true will automatically detect the AAD tenantId for your keyvault. This is useful during AAD tenant migration of subscription.
  • View secrets
kubectl get secrets

Logs

  • View init container logs:
kubectl logs <Pod ID> -c keyvault-agent