Plug in CA Certificates

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This task shows how administrators can configure the Istio certificate authority (CA) with a root certificate, signing certificate and key.

By default the Istio CA generates a self-signed root certificate and key and uses them to sign the workload certificates. To protect the root CA key, you should use a root CA which runs on a secure machine offline, and use the root CA to issue intermediate certificates to the Istio CAs that run in each cluster. An Istio CA can sign workload certificates using the administrator-specified certificate and key, and distribute an administrator-specified root certificate to the workloads as the root of trust.

The following graph demonstrates the recommended CA hierarchy in a mesh containing two clusters.

This task demonstrates how to generate and plug in the certificates and key for the Istio CA. These steps can be repeated to provision certificates and keys for Istio CAs running in each cluster.

Plug in certificates and key into the cluster

In the top-level directory of the Istio installation package, create a directory to hold certificates and keys:
```
$ mkdir -p certs
$ pushd certs
```
Generate the root certificate and key:
```
$ make -f ../tools/certs/Makefile.selfsigned.mk root-ca
```
This will generate the following files:
- root-cert.pem: the generated root certificate
- root-key.pem: the generated root key
- root-ca.conf: the configuration for openssl to generate the root certificate
- root-cert.csr: the generated CSR for the root certificate
For each cluster, generate an intermediate certificate and key for the Istio CA. The following is an example for cluster1:
```
$ make -f ../tools/certs/Makefile.selfsigned.mk cluster1-cacerts
```
This will generate the following files in a directory named cluster1:
- ca-cert.pem: the generated intermediate certificates
- ca-key.pem: the generated intermediate key
- cert-chain.pem: the generated certificate chain which is used by istiod
- root-cert.pem: the root certificate
You can replace cluster1 with a string of your choosing. For example, with the argument cluster2-cacerts, you can create certificates and key in a directory called cluster2.
If you are doing this on an offline machine, copy the generated directory to a machine with access to the clusters.

In each cluster, create a secret cacerts including all the input files ca-cert.pem, ca-key.pem, root-cert.pem and cert-chain.pem. For example, for cluster1:

$ kubectl create namespace istio-system
$ kubectl create secret generic cacerts -n istio-system \
      --from-file=cluster1/ca-cert.pem \
      --from-file=cluster1/ca-key.pem \
      --from-file=cluster1/root-cert.pem \
      --from-file=cluster1/cert-chain.pem

Return to the top-level directory of the Istio installation:
```
$ popd
```

Deploy Istio

Deploy Istio using the demo profile.
Istio’s CA will read certificates and key from the secret-mount files.
```
$ istioctl install --set profile=demo
```

Deploying example services

Deploy the httpbin and curl sample services.

$ kubectl create ns foo
$ kubectl apply -f <(istioctl kube-inject -f samples/httpbin/httpbin.yaml) -n foo
$ kubectl apply -f <(istioctl kube-inject -f samples/curl/curl.yaml) -n foo

Deploy a policy for workloads in the foo namespace to only accept mutual TLS traffic.

$ kubectl apply -n foo -f - <<EOF
apiVersion: security.istio.io/v1
kind: PeerAuthentication
metadata:
  name: "default"
spec:
  mtls:
    mode: STRICT
EOF

Verifying the certificates

In this section, we verify that workload certificates are signed by the certificates that we plugged into the CA. This requires you have openssl installed on your machine.

Sleep 20 seconds for the mTLS policy to take effect before retrieving the certificate chain of httpbin. As the CA certificate used in this example is self-signed, the verify error:num=19:self signed certificate in certificate chain error returned by the openssl command is expected.
```
$ sleep 20; kubectl exec "$(kubectl get pod -l app=curl -n foo -o jsonpath={.items..metadata.name})" -c istio-proxy -n foo -- openssl s_client -showcerts -connect httpbin.foo:8000 > httpbin-proxy-cert.txt
```

Parse the certificates on the certificate chain.

$ sed -n '/-----BEGIN CERTIFICATE-----/{:start /-----END CERTIFICATE-----/!{N;b start};/.*/p}' httpbin-proxy-cert.txt > certs.pem
$ awk 'BEGIN {counter=0;} /BEGIN CERT/{counter++} { print > "proxy-cert-" counter ".pem"}' < certs.pem

Verify the root certificate is the same as the one specified by the administrator:

$ openssl x509 -in certs/cluster1/root-cert.pem -text -noout > /tmp/root-cert.crt.txt
$ openssl x509 -in ./proxy-cert-3.pem -text -noout > /tmp/pod-root-cert.crt.txt
$ diff -s /tmp/root-cert.crt.txt /tmp/pod-root-cert.crt.txt
Files /tmp/root-cert.crt.txt and /tmp/pod-root-cert.crt.txt are identical

Verify the CA certificate is the same as the one specified by the administrator:

$ openssl x509 -in certs/cluster1/ca-cert.pem -text -noout > /tmp/ca-cert.crt.txt
$ openssl x509 -in ./proxy-cert-2.pem -text -noout > /tmp/pod-cert-chain-ca.crt.txt
$ diff -s /tmp/ca-cert.crt.txt /tmp/pod-cert-chain-ca.crt.txt
Files /tmp/ca-cert.crt.txt and /tmp/pod-cert-chain-ca.crt.txt are identical

Verify the certificate chain from the root certificate to the workload certificate:

$ openssl verify -CAfile <(cat certs/cluster1/ca-cert.pem certs/cluster1/root-cert.pem) ./proxy-cert-1.pem
./proxy-cert-1.pem: OK

Cleanup

Remove the certificates, keys, and intermediate files from your local disk:
```
$ rm -rf certs
```

Remove the secret cacerts:

$ kubectl delete secret cacerts -n istio-system

Remove the authentication policy from the foo namespace:

$ kubectl delete peerauthentication -n foo default

Remove the sample applications curl and httpbin:

$ kubectl delete -f samples/curl/curl.yaml -n foo
$ kubectl delete -f samples/httpbin/httpbin.yaml -n foo

Uninstall Istio from the cluster:
```
$ istioctl uninstall --purge -y
```
Remove the namespace foo and istio-system from the cluster:
```
$ kubectl delete ns foo istio-system
```