---
title: Generate Certificates Manually
content_type: task
weight: 30
---
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When using client certificate authentication, you can generate certificates
manually through [`easyrsa`](https://github.com/OpenVPN/easy-rsa), [`openssl`](https://github.com/openssl/openssl) or [`cfssl`](https://github.com/cloudflare/cfssl).
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### easyrsa
**easyrsa** can manually generate certificates for your cluster.
1. Download, unpack, and initialize the patched version of `easyrsa3`.
```shell
curl -LO https://dl.k8s.io/easy-rsa/easy-rsa.tar.gz
tar xzf easy-rsa.tar.gz
cd easy-rsa-master/easyrsa3
./easyrsa init-pki
```
1. Generate a new certificate authority (CA). `--batch` sets automatic mode;
`--req-cn` specifies the Common Name (CN) for the CA's new root certificate.
```shell
./easyrsa --batch "--req-cn=${MASTER_IP}@`date +%s`" build-ca nopass
```
1. Generate server certificate and key.
The argument `--subject-alt-name` sets the possible IPs and DNS names the API server will
be accessed with. The `MASTER_CLUSTER_IP` is usually the first IP from the service CIDR
that is specified as the `--service-cluster-ip-range` argument for both the API server and
the controller manager component. The argument `--days` is used to set the number of days
after which the certificate expires.
The sample below also assumes that you are using `cluster.local` as the default
DNS domain name.
```shell
./easyrsa --subject-alt-name="IP:${MASTER_IP},"\
"IP:${MASTER_CLUSTER_IP},"\
"DNS:kubernetes,"\
"DNS:kubernetes.default,"\
"DNS:kubernetes.default.svc,"\
"DNS:kubernetes.default.svc.cluster,"\
"DNS:kubernetes.default.svc.cluster.local" \
--days=10000 \
build-server-full server nopass
```
1. Copy `pki/ca.crt`, `pki/issued/server.crt`, and `pki/private/server.key` to your directory.
1. Fill in and add the following parameters into the API server start parameters:
```shell
--client-ca-file=/yourdirectory/ca.crt
--tls-cert-file=/yourdirectory/server.crt
--tls-private-key-file=/yourdirectory/server.key
```
### openssl
**openssl** can manually generate certificates for your cluster.
1. Generate a ca.key with 2048bit:
```shell
openssl genrsa -out ca.key 2048
```
1. According to the ca.key generate a ca.crt (use `-days` to set the certificate effective time):
```shell
openssl req -x509 -new -nodes -key ca.key -subj "/CN=${MASTER_IP}" -days 10000 -out ca.crt
```
1. Generate a server.key with 2048bit:
```shell
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 assumes that you are using `cluster.local` as the default
DNS domain name.
```ini
[ 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:
```shell
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:
```shell
openssl x509 -req -in server.csr -CA ca.crt -CAkey ca.key \
-CAcreateserial -out server.crt -days 10000 \
-extensions v3_ext -extfile csr.conf -sha256
```
1. View the certificate signing request:
```shell
openssl req -noout -text -in ./server.csr
```
1. View the certificate:
```shell
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.
```shell
curl -L https://github.com/cloudflare/cfssl/releases/download/v1.5.0/cfssl_1.5.0_linux_amd64 -o cfssl
chmod +x cfssl
curl -L https://github.com/cloudflare/cfssl/releases/download/v1.5.0/cfssljson_1.5.0_linux_amd64 -o cfssljson
chmod +x cfssljson
curl -L https://github.com/cloudflare/cfssl/releases/download/v1.5.0/cfssl-certinfo_1.5.0_linux_amd64 -o cfssl-certinfo
chmod +x cfssl-certinfo
```
1. Create a directory to hold the artifacts and initialize cfssl:
```shell
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`:
```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 to replace the values marked with angle brackets with
real values you want to use.
```json
{
"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`):
```shell
../cfssl gencert -initca ca-csr.json | ../cfssljson -bare ca
```
1. Create a JSON config file for generating keys and certificates for the API
server, for example, `server-csr.json`. 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 assumes that you are using `cluster.local` as the default
DNS domain name.
```json
{
"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:
```shell
../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:
```shell
sudo cp ca.crt /usr/local/share/ca-certificates/kubernetes.crt
sudo update-ca-certificates
```
```none
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
in the [Managing TLS in a cluster](/docs/tasks/tls/managing-tls-in-a-cluster)
task page.