---
title: Certificates
content_template: templates/concept
weight: 20
---


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When using client certificate authentication, you can generate certificates
manually through `easyrsa`, `openssl` or `cfssl`.

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### easyrsa

**easyrsa** can manually generate certificates for your cluster.

1.  Download, unpack, and initialize the patched version of easyrsa3.

        curl -LO https://storage.googleapis.com/kubernetes-release/easy-rsa/easy-rsa.tar.gz
        tar xzf easy-rsa.tar.gz
        cd easy-rsa-master/easyrsa3
        ./easyrsa init-pki
1.  Generate a CA. (`--batch` set automatic mode. `--req-cn` default CN to use.)

        ./easyrsa --batch "--req-cn=${MASTER_IP}@`date +%s`" build-ca nopass
1.  Generate server certificate and key.
    The argument `--subject-alt-name` sets the possible IPs and DNS names the API server will
    be accessed with. The `MASTER_CLUSTER_IP` is usually the first IP from the service CIDR
    that is specified as the `--service-cluster-ip-range` argument for both the API server and
    the controller manager component. The argument `--days` is used to set the number of days
    after which the certificate expires.
    The sample below also assume that you are using `cluster.local` as the default
    DNS domain name.

        ./easyrsa --subject-alt-name="IP:${MASTER_IP},"\
        "IP:${MASTER_CLUSTER_IP},"\
        "DNS:kubernetes,"\
        "DNS:kubernetes.default,"\
        "DNS:kubernetes.default.svc,"\
        "DNS:kubernetes.default.svc.cluster,"\
        "DNS:kubernetes.default.svc.cluster.local" \
        --days=10000 \
        build-server-full server nopass
1.  Copy `pki/ca.crt`, `pki/issued/server.crt`, and `pki/private/server.key` to your directory.
1.  Fill in and add the following parameters into the API server start parameters:

        --client-ca-file=/yourdirectory/ca.crt
        --tls-cert-file=/yourdirectory/server.crt
        --tls-private-key-file=/yourdirectory/server.key

### openssl

**openssl** can manually generate certificates for your cluster.

1.  Generate a ca.key with 2048bit:

        openssl genrsa -out ca.key 2048
1.  According to the ca.key generate a ca.crt (use -days to set the certificate effective time):

        openssl req -x509 -new -nodes -key ca.key -subj "/CN=${MASTER_IP}" -days 10000 -out ca.crt
1.  Generate a server.key with 2048bit:

        openssl genrsa -out server.key 2048
1.  Create a config file for generating a Certificate Signing Request (CSR).
    Be sure to substitute the values marked with angle brackets (e.g. `<MASTER_IP>`)
    with real values before saving this to a file (e.g. `csr.conf`).
    Note that the value for `MASTER_CLUSTER_IP` is the service cluster IP for the
    API server as described in previous subsection.
    The sample below also assume that you are using `cluster.local` as the default
    DNS domain name.

        [ req ]
        default_bits = 2048
        prompt = no
        default_md = sha256
        req_extensions = req_ext
        distinguished_name = dn
        
        [ dn ]
        C = <country>
        ST = <state>
        L = <city>
        O = <organization>
        OU = <organization unit>
        CN = <MASTER_IP>
        
        [ req_ext ]
        subjectAltName = @alt_names
        
        [ alt_names ]
        DNS.1 = kubernetes
        DNS.2 = kubernetes.default
        DNS.3 = kubernetes.default.svc
        DNS.4 = kubernetes.default.svc.cluster
        DNS.5 = kubernetes.default.svc.cluster.local
        IP.1 = <MASTER_IP>
        IP.2 = <MASTER_CLUSTER_IP>
        
        [ v3_ext ]
        authorityKeyIdentifier=keyid,issuer:always
        basicConstraints=CA:FALSE
        keyUsage=keyEncipherment,dataEncipherment
        extendedKeyUsage=serverAuth,clientAuth
        subjectAltName=@alt_names
1.  Generate the certificate signing request based on the config file:

        openssl req -new -key server.key -out server.csr -config csr.conf
1.  Generate the server certificate using the ca.key, ca.crt and server.csr:

        openssl x509 -req -in server.csr -CA ca.crt -CAkey ca.key \
        -CAcreateserial -out server.crt -days 10000 \
        -extensions v3_ext -extfile csr.conf
1.  View the certificate:

        openssl x509  -noout -text -in ./server.crt

Finally, add the same parameters into the API server start parameters.

### cfssl

**cfssl** is another tool for certificate generation.

1.  Download, unpack and prepare the command line tools as shown below.
    Note that you may need to adapt the sample commands based on the hardware
    architecture and cfssl version you are using.

        curl -L https://pkg.cfssl.org/R1.2/cfssl_linux-amd64 -o cfssl
        chmod +x cfssl
        curl -L https://pkg.cfssl.org/R1.2/cfssljson_linux-amd64 -o cfssljson
        chmod +x cfssljson
        curl -L https://pkg.cfssl.org/R1.2/cfssl-certinfo_linux-amd64 -o cfssl-certinfo
        chmod +x cfssl-certinfo
1.  Create a directory to hold the artifacts and initialize cfssl:

        mkdir cert
        cd cert
        ../cfssl print-defaults config > config.json
        ../cfssl print-defaults csr > csr.json
1.  Create a JSON config file for generating the CA file, for example, `ca-config.json`:

        {
          "signing": {
            "default": {
              "expiry": "8760h"
            },
            "profiles": {
              "kubernetes": {
                "usages": [
                  "signing",
                  "key encipherment",
                  "server auth",
                  "client auth"
                ],
                "expiry": "8760h"
              }
            }
          }
        }
1.  Create a JSON config file for CA certificate signing request (CSR), for example,
    `ca-csr.json`. Be sure the replace the values marked with angle brackets with
    real values you want to use.

        {
          "CN": "kubernetes",
          "key": {
            "algo": "rsa",
            "size": 2048
          },
          "names":[{
            "C": "<country>",
            "ST": "<state>",
            "L": "<city>",
            "O": "<organization>",
            "OU": "<organization unit>"
          }]
        }
1.  Generate CA key (`ca-key.pem`) and certificate (`ca.pem`):

        ../cfssl gencert -initca ca-csr.json | ../cfssljson -bare ca
1.  Create a JSON config file for generating keys and certificates for the API
    server as shown below. Be sure to replace the values in angle brackets with
    real values you want to use. The `MASTER_CLUSTER_IP` is the service cluster
    IP for the API server as described in previous subsection.
    The sample below also assume that you are using `cluster.local` as the default
    DNS domain name.

        {
          "CN": "kubernetes",
          "hosts": [
            "127.0.0.1",
            "<MASTER_IP>",
            "<MASTER_CLUSTER_IP>",
            "kubernetes",
            "kubernetes.default",
            "kubernetes.default.svc",
            "kubernetes.default.svc.cluster",
            "kubernetes.default.svc.cluster.local"
          ],
          "key": {
            "algo": "rsa",
            "size": 2048
          },
          "names": [{
            "C": "<country>",
            "ST": "<state>",
            "L": "<city>",
            "O": "<organization>",
            "OU": "<organization unit>"
          }]
        } 
1.  Generate the key and certificate for the API server, which are by default
    saved into file `server-key.pem` and `server.pem` respectively:

        ../cfssl gencert -ca=ca.pem -ca-key=ca-key.pem \
        --config=ca-config.json -profile=kubernetes \
        server-csr.json | ../cfssljson -bare server


## Distributing Self-Signed CA Certificate

A client node may refuse to recognize a self-signed CA certificate as valid.
For a non-production deployment, or for a deployment that runs behind a company
firewall, you can distribute a self-signed CA certificate to all clients and
refresh the local list for valid certificates.

On each client, perform the following operations:

```bash
$ sudo cp ca.crt /usr/local/share/ca-certificates/kubernetes.crt
$ sudo update-ca-certificates
Updating certificates in /etc/ssl/certs...
1 added, 0 removed; done.
Running hooks in /etc/ca-certificates/update.d....
done.
```

## Certificates API

You can use the `certificates.k8s.io` API to provision
x509 certificates to use for authentication as documented
[here](/docs/tasks/tls/managing-tls-in-a-cluster).

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