mTLS and Certificate Issuance

Open Service Mesh uses mTLS for encryption of data between pods as well as Envoy and service identity. Certificates are created and distributed to each Envoy proxy via the SDS protocol by the OSM control plane.

Types of Certificates

There are a few kinds of certificates used in OSM:

Cert Type	Where it is issued	How it is used	Validity duration	Sample CommonName
xDS bootstrap	pkg/injector/patch.go → createPatch()	used for Envoy-to-xDS connections; identifies Envoy (Pod) to the xDS control plane.	XDSCertificateValidityPeriod → a decade	`7b2359d7-f201-4d3f-a217-73fd6e44e39b.bookstore-v2.bookstore`
service	pkg/envoy/sds/response.go → createDiscoveryResponse()	used for east-west communication between Envoys; identifies Service Accounts	defined in ConfigMap; default 24h	`bookstore-v2.bookstore.cluster.local`
mutating webhook handler	pkg/injector/webhook.go → NewWebhook()	used by the webhook handler; note: this cert does not have to be related to the Envoy certs, but it does have to match the CA in the MutatingWebhookConfiguration	XDSCertificateValidityPeriod → a decade	`osm-controller.osm-system.svc`
validating webhook handler	pkg/configurator/validating_webhook.go → NewValidatingWebhook()	used by the validating webhook handler; (same note as MWH cert)	XDSCertificateValidityPeriod → a decade	`osm-config-validator.osm-system.svc`

Root Certificate

The root certificate for the service mesh is stored in an Opaque Kubernetes Secret named osm-ca-bundle in the OSM Namespace (in most cases osm-system). The secret YAML has the following shape:

apiVersion: v1
kind: Secret
type: Opaque
metadata:
      name: osm-ca-bundle
      namespace: osm-system
data:
  ca.crt: <base64 encoded root cert>
  expiration: <base64 encoded ISO 8601 certificate expiration date; for example: 2031-01-11T23:15:09.299Z> 
  private.key: <base64 encoded private key>

For details and code where this is used see osm-controller.go.

Issuing Certificates

Open Service Mesh supports 4 methods of issuing certificates:

using an internal OSM package, called Tresor. This is the default for a first time installation.
using Hashicorp Vault
using Azure Key Vault
using cert-manager

Using OSM’s Tresor certificate issuer

Open Service Mesh includes a package, tresor. This is a minimal implementation of the certificate.Manager interface. It issues certificates leveraging the crypto Go library, and stores these certificates as Kubernetes secrets.

To use the tresor package during development set export CERT_MANAGER=tresor in the .env file of this repo.
To use this package in your Kubernetes cluster set the CERT_MANAGER=tresor variable in the Helm chart prior to deployment.

Additionally:

--ca-bundle-secret-name - this string is the name of the Kubernetes secret, where the CA root certificate and private key will be saved.

Using Hashicorp Vault

Service Mesh operators, who consider storing their service mesh’s CA root key in Kubernetes insecure have the option to integrate with a Hashicorp Vault installation. In such scenarios a pre-configured Hashi Vault is required. Open Service Mesh’s control plane connects to the URL of the Vault, authenticates, and begins requesting certificates. This setup shifts the responsibility of correctly and securely configuring Vault to the operator.

The following configuration parameters will be required for OSM to integrate with an existing Vault installation:

Vault address
Vault token
Validity period for certificates

CLI flags control how OSM integrates with Vault. The following OSM command line parameters must be configured to issue certificates with Vault:

--certificate-manager - set this to vault
--vault-host - host name of the Vault server (example: vault.contoso.com)
--vault-protocol - protocol for Vault connection (http or https)
--vault-token - token to be used by OSM to connect to Vault (this is issued on the Vault server for the particular role)
--vault-role - role created on Vault server and dedicated to Open Service Mesh (example: openservicemesh)
--service-cert-validity-duration - period for which each new certificate issued for service-to-service communication will be valid. It is represented as a sequence of decimal numbers each with optional fraction and a unit suffix, ex: 1h to represent 1 hour, 30m to represent 30 minutes, 1.5h or 1h30m to represent 1 hour and 30 minutes.

Additionally:

--ca-bundle-secret-name - this string is the name of the Kubernetes secret where the service mesh root certificate will be stored. When using Vault (unlike Tresor) the root key will not be exported to this secret.

Installing Hashi Vault

Installation of Hashi Vault is out of scope for the Open Service Mesh project. Typically this is the responsibility of dedicated security teams. Documentation on how to deploy Vault securely and make it highly available is available on Vault’s website.

This repository does contain a script (deploy-vault.sh), which is used to automate the deployment of Hashi Vault for continuous integration. This is strictly for development purposes only. Running the script will deploy Vault in a Kubernetes namespace defined by the $K8S_NAMESPACE environment variable in your .env file. This script can be used for demonstration purposes. It requires the following environment variables:

export K8S_NAMESPACE=osm-system-ns
export VAULT_TOKEN=xyz

Running the ./demo/deploy-vault.sh script will result in a dev Vault installation:

NAMESPACE         NAME                                    READY   STATUS    RESTARTS   AGE
osm-system-ns     vault-5f678c4cc5-9wchj                  1/1     Running   0          28s

Fetching the logs of the pod will show details on the Vault installation:

==> Vault server configuration:

             Api Address: http://0.0.0.0:8200
                     Cgo: disabled
         Cluster Address: https://0.0.0.0:8201
              Listener 1: tcp (addr: "0.0.0.0:8200", cluster address: "0.0.0.0:8201", max_request_duration: "1m30s", max_request_size: "33554432", tls: "disabled")
               Log Level: info
                   Mlock: supported: true, enabled: false
           Recovery Mode: false
                 Storage: inmem
                 Version: Vault v1.4.0

WARNING! dev mode is enabled! In this mode, Vault runs entirely in-memory
and starts unsealed with a single unseal key. The root token is already
authenticated to the CLI, so you can immediately begin using Vault.

You may need to set the following environment variable:

    $ export VAULT_ADDR='http://0.0.0.0:8200'

The unseal key and root token are displayed below in case you want to
seal/unseal the Vault or re-authenticate.

Unseal Key: cZzYxUaJaN10sa2UrPu7akLoyU6rKSXMcRt5dbIKlZ0=
Root Token: xyz

Development mode should NOT be used in production installations!

==> Vault server started! Log data will stream in below:
...

The outcome of deploying Vault in your system is a URL and a token. For instance the URL of Vauld could be http://vault.osm-system-ns.svc.cluster.local and the token xxx.

Configure OSM with Vault

After Vault installation and before we use Helm to deploy OSM, the following parameters must be provided provided in the Helm chart:

CERT_MANAGER=vault
VAULT_HOST="vault.${K8S_NAMESPACE}.svc.cluster.local"
VAULT_PROTOCOL=http
VAULT_TOKEN=xyz
VAULT_ROLE=openservicemesh

When running OSM on your local workstation, use the following CLI parameters:

--certificate-manager="vault"
--vault-host="localhost"  # or the host where Vault is installed
--vault-protocol="http"
--vault-token="xyz"
--vault-role="openservicemesh'
--service-cert-validity-duration=24h

How OSM Integrates with Vault

When the OSM control plane starts, a new certificate issuer is instantiated. The kind of cert issuer is determined by the --certificate-manager CLI parameter. When this is set to vault OSM uses a Vault cert issuer. This is a Hashicorp Vault client, which satisfies the certificate.Manager interface. It provides the following methods:

  - IssueCertificate - issues new certificates
  - GetCertificate - retrieves a certificate given its Common Name (CN)
  - RotateCertificate - rotates expiring certificates
  - GetAnnouncementsChannel - returns a channel, which is used to announce when certificates have been issued or rotated

OSM assumes that a CA has already been created on the Vault server. OSM also requires a dedicated Vault role (for instance pki/roles/openservicemesh). The Vault role created by the ./demo/deploy-vault.sh script applies the following configuration, which is only appropriate for development purposes:

allow_any_name: true
allow_subdomains: true
allow_baredomains: true
allow_localhost: true
max_ttl: 24h

Hashi Vault’s site has excellent documentation on how to create a new CA. The ./demo/deploy-vault.sh script uses the following commands to setup the dev environment:

export VAULT_TOKEN="xyz"
export VAULT_ADDR="http://localhost:8200"
export VAULT_ROLE="openservicemesh

# Launch the Vault server in dev mode
vault server -dev -dev-listen-address=0.0.0.0:8200 -dev-root-token-id=${VAULT_TOKEN}

# Also save the token locally so this is available
echo $VAULT_TOKEN>~/.vault-token;

# Enable the PKI secrets engine (See: https://www.vaultproject.io/docs/secrets/pki#pki-secrets-engine)
vault secrets enable pki;

# Set the max lease TTL to a decade
vault secrets tune -max-lease-ttl=87600h pki;

# Set URL configuration (See: https://www.vaultproject.io/docs/secrets/pki#set-url-configuration)
vault write pki/config/urls issuing_certificates='http://127.0.0.1:8200/v1/pki/ca' crl_distribution_points='http://127.0.0.1:8200/v1/pki/crl';

# Configure a role named "openservicemesh" (See: https://www.vaultproject.io/docs/secrets/pki#configure-a-role)
vault write pki/roles/${VAULT_ROLE} allow_any_name=true allow_subdomains=true;

# Create a root certificate named "osm.root" (See: https://www.vaultproject.io/docs/secrets/pki#setup)
vault write pki/root/generate/internal common_name='osm.root' ttl='87600h'

The OSM control plane provides verbose logs on operations done with the Vault installations.

Using cert-manager

cert-manager is another provider for issuing signed certificates to the OSM service mesh, without the need for storing private keys in Kubernetes. cert-manager has support for multiple issuer backends core to cert-manager, as well as pluggable external issuers.

Note that ACME certificates are not supported as an issuer for service mesh certificates.

When OSM requests certificates, it will create cert-manager CertificateRequest resources that are signed by the configured issuer.

Configure cert-manger for OSM signing

cert-manager must first be installed, with an issuer ready, before OSM can be installed using cert-manager as the certificate provider. You can find the installation documentation for cert-manager here.

Once cert-manager is installed, configure an issuer resource to serve certificate requests. It is recommended to use an Issuer resource kind (rather than a ClusterIssuer) which should live in the OSM namespace (osm-system by default).

Once ready, it is required to store the root CA certificate of your issuer as a Kubernetes secret in the OSM namespace (osm-system by default) at the ca.crt key. The target CA secret name can be configured on OSM with the flag --ca-bundle-secret-name (typically osm-ca-bundle).

kubectl create secret -n osm-system generic osm-ca-bundle --from-file ca.tls

Configure OSM with cert-manager

In order for OSM to use cert-manager with the configured issuer, set the following CLI arguments on the osm install command:

--certificate-manager="cert-manager" - Required to use cert-manager as the provider.
--cert-manager-issuer-name - The name of the [Cluster]Issuer resource (defaulted to osm-ca).
--cert-manager-issuer-kind - The kind of issuer (either Issuer or ClusterIssuer, defaulted to Issuer).
--cert-manager-issuer-group - The group that the issuer belongs to (defaulted to cert-manager.io which is all core issuer types).

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