创建 CA 证书和秘钥

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2023-12-01

kubernetes 系统各组件需要使用 TLS 证书对通信进行加密，本文档使用 CloudFlare 的 PKI 工具集 cfssl 来生成 Certificate Authority (CA) 证书和秘钥文件，CA 是自签名的证书，用来签名后续创建的其它 TLS 证书。

安装 `CFSSL`

$ wget https://pkg.cfssl.org/R1.2/cfssl_linux-amd64
$ chmod +x cfssl_linux-amd64
$ sudo mv cfssl_linux-amd64 /root/local/bin/cfssl

$ wget https://pkg.cfssl.org/R1.2/cfssljson_linux-amd64
$ chmod +x cfssljson_linux-amd64
$ sudo mv cfssljson_linux-amd64 /root/local/bin/cfssljson

$ wget https://pkg.cfssl.org/R1.2/cfssl-certinfo_linux-amd64
$ chmod +x cfssl-certinfo_linux-amd64
$ sudo mv cfssl-certinfo_linux-amd64 /root/local/bin/cfssl-certinfo

$ export PATH=/root/local/bin:$PATH
$ mkdir ssl
$ cd ssl
$ cfssl print-defaults config > config.json
$ cfssl print-defaults csr > csr.json
$

创建 CA (Certificate Authority)

创建 CA 配置文件：

$ cat ca-config.json
{
  "signing": {
    "default": {
      "expiry": "8760h"
    },
    "profiles": {
      "kubernetes": {
        "usages": [
            "signing",
            "key encipherment",
            "server auth",
            "client auth"
        ],
        "expiry": "8760h"
      }
    }
  }
}

ca-config.json：可以定义多个 profiles，分别指定不同的过期时间、使用场景等参数；后续在签名证书时使用某个 profile；
signing：表示该证书可用于签名其它证书；生成的 ca.pem 证书中 CA=TRUE；
server auth：表示 client 可以用该 CA 对 server 提供的证书进行验证；
client auth：表示 server 可以用该 CA 对 client 提供的证书进行验证；

创建 CA 证书签名请求：

$ cat ca-csr.json
{
  "CN": "kubernetes",
  "key": {
    "algo": "rsa",
    "size": 2048
  },
  "names": [
    {
      "C": "CN",
      "ST": "BeiJing",
      "L": "BeiJing",
      "O": "k8s",
      "OU": "System"
    }
  ]
}

"CN"：Common Name，kube-apiserver 从证书中提取该字段作为请求的用户名 (User Name)；浏览器使用该字段验证网站是否合法；
"O"：Organization，kube-apiserver 从证书中提取该字段作为请求用户所属的组 (Group)；

生成 CA 证书和私钥：

$ cfssl gencert -initca ca-csr.json | cfssljson -bare ca
$ ls ca*
ca-config.json  ca.csr  ca-csr.json  ca-key.pem  ca.pem
$

分发证书

将生成的 CA 证书、秘钥文件、配置文件拷贝到所有机器的 /etc/kubernetes/ssl 目录下

$ sudo mkdir -p /etc/kubernetes/ssl
$ sudo cp ca* /etc/kubernetes/ssl
$

校验证书

以校验 kubernetes 证书(后续部署 master 节点时生成的)为例：

使用 `openssl` 命令

$ openssl x509  -noout -text -in  kubernetes.pem
...
    Signature Algorithm: sha256WithRSAEncryption
        Issuer: C=CN, ST=BeiJing, L=BeiJing, O=k8s, OU=System, CN=Kubernetes
        Validity
            Not Before: Apr  5 05:36:00 2017 GMT
            Not After : Apr  5 05:36:00 2018 GMT
        Subject: C=CN, ST=BeiJing, L=BeiJing, O=k8s, OU=System, CN=kubernetes
...
        X509v3 extensions:
            X509v3 Key Usage: critical
                Digital Signature, Key Encipherment
            X509v3 Extended Key Usage:
                TLS Web Server Authentication, TLS Web Client Authentication
            X509v3 Basic Constraints: critical
                CA:FALSE
            X509v3 Subject Key Identifier:
                DD:52:04:43:10:13:A9:29:24:17:3A:0E:D7:14:DB:36:F8:6C:E0:E0
            X509v3 Authority Key Identifier:
                keyid:44:04:3B:60:BD:69:78:14:68:AF:A0:41:13:F6:17:07:13:63:58:CD

            X509v3 Subject Alternative Name:
                DNS:kubernetes, DNS:kubernetes.default, DNS:kubernetes.default.svc, DNS:kubernetes.default.svc.cluster, DNS:kubernetes.default.svc.cluster.local, IP Address:127.0.0.1, IP Address:10.64.3.7, IP Address:10.254.0.1
...

确认 Issuer 字段的内容和 ca-csr.json 一致；
确认 Subject 字段的内容和 kubernetes-csr.json 一致；
确认 X509v3 Subject Alternative Name 字段的内容和 kubernetes-csr.json 一致；
确认 X509v3 Key Usage、Extended Key Usage 字段的内容和 ca-config.json 中 kubernetes profile 一致；

使用 `cfssl-certinfo` 命令

$ cfssl-certinfo -cert kubernetes.pem
...
{
  "subject": {
    "common_name": "kubernetes",
    "country": "CN",
    "organization": "k8s",
    "organizational_unit": "System",
    "locality": "BeiJing",
    "province": "BeiJing",
    "names": [
      "CN",
      "BeiJing",
      "BeiJing",
      "k8s",
      "System",
      "kubernetes"
    ]
  },
  "issuer": {
    "common_name": "Kubernetes",
    "country": "CN",
    "organization": "k8s",
    "organizational_unit": "System",
    "locality": "BeiJing",
    "province": "BeiJing",
    "names": [
      "CN",
      "BeiJing",
      "BeiJing",
      "k8s",
      "System",
      "Kubernetes"
    ]
  },
  "serial_number": "174360492872423263473151971632292895707129022309",
  "sans": [
    "kubernetes",
    "kubernetes.default",
    "kubernetes.default.svc",
    "kubernetes.default.svc.cluster",
    "kubernetes.default.svc.cluster.local",
    "127.0.0.1",
    "10.64.3.7",
    "10.64.3.8",
    "10.66.3.86",
    "10.254.0.1"
  ],
  "not_before": "2017-04-05T05:36:00Z",
  "not_after": "2018-04-05T05:36:00Z",
  "sigalg": "SHA256WithRSA",
...

参考

Generate self-signed certificates
Setting up a Certificate Authority and Creating TLS Certificates
Client Certificates V/s Server Certificates