Generate x509 certs using Ruby

ca.rb

require 'openssl'
OpenSSL::Random.seed File.read('/dev/random', 16)

root_key = OpenSSL::PKey::RSA.new 2048 # the CA's public/private key
root_ca = OpenSSL::X509::Certificate.new

root_ca.version = 2 # cf. RFC 5280 - to make it a "v3" certificate
root_ca.serial = 1
root_ca.subject = OpenSSL::X509::Name.parse "/CN=kube-ca"
root_ca.issuer = root_ca.subject # root CA's are "self-signed"
root_ca.public_key = root_key.public_key
root_ca.not_before = Time.now
root_ca.not_after = root_ca.not_before + 2 * 365 * 24 * 60 * 60 # 2 years validity
ef = OpenSSL::X509::ExtensionFactory.new
ef.subject_certificate = root_ca
ef.issuer_certificate = root_ca
root_ca.add_extension(ef.create_extension("basicConstraints","CA:TRUE",true))
root_ca.add_extension(ef.create_extension("keyUsage","keyCertSign, cRLSign", true))
root_ca.add_extension(ef.create_extension("subjectKeyIdentifier","hash",false))
root_ca.add_extension(ef.create_extension("authorityKeyIdentifier","keyid:always",false))
root_ca.sign(root_key, OpenSSL::Digest::SHA256.new)

File.open 'tmp/ca.key', 'wb' do |f|
  f.write root_key.export(nil, nil)
end

File.open 'tmp/ca.crt', 'wb' do |f|
  f.write root_ca.to_pem
end

server.rb

require 'openssl'
OpenSSL::Random.seed File.read('/dev/random', 16)

root_key = OpenSSL::PKey::RSA.new File.read('tmp/ca.key')
root_ca = OpenSSL::X509::Certificate.new(File.read('tmp/ca.crt'))

key = OpenSSL::PKey::RSA.new 2048
cert = OpenSSL::X509::Certificate.new
cert.version = 2
cert.serial = 2
cert.subject = OpenSSL::X509::Name.parse "/CN=kube-client"
cert.issuer = root_ca.subject # root CA is the issuer
cert.public_key = key.public_key
cert.not_before = Time.now
cert.not_after = cert.not_before + 1 * 365 * 24 * 60 * 60 # 1 years validity
ef = OpenSSL::X509::ExtensionFactory.new
ef.subject_certificate = cert
ef.issuer_certificate = root_ca
cert.add_extension(ef.create_extension("basicConstraints","CA:FALSE",true))
cert.add_extension(ef.create_extension("keyUsage","nonRepudiation, digitalSignature, keyEncipherment", true))
cert.add_extension(ef.create_extension("extendedKeyUsage","clientAuth, serverAuth",true))
cert.add_extension(ef.create_extension("subjectAltName","DNS:kubernetes,DNS:kubernetes.default,DNS:kubernetes.default.svc,DNS:kubernetes.default.svc.cluster.local",true))
cert.sign(root_key, OpenSSL::Digest::SHA256.new)

File.open 'tmp/server.key', 'wb' do |f|
  f.write key.export(nil, nil)
end

File.open 'tmp/server.crt', 'wb' do |f|
  f.write cert.to_pem
end