core/internal/kubernetes/apiserver.go

// Copyright 2020 The Monogon Project Authors.
//
// SPDX-License-Identifier: Apache-2.0
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

package kubernetes

import (
	"context"
	"encoding/pem"
	"fmt"
	"io"
	"net"
	"os/exec"

	"git.monogon.dev/source/nexantic.git/core/internal/common"
	"git.monogon.dev/source/nexantic.git/core/internal/common/supervisor"
	"git.monogon.dev/source/nexantic.git/core/internal/kubernetes/pki"
	"git.monogon.dev/source/nexantic.git/core/pkg/fileargs"

	"go.etcd.io/etcd/clientv3"
)

type apiserverConfig struct {
	advertiseAddress net.IP
	serviceIPRange   net.IPNet
	// All PKI-related things are in DER
	idCA                  []byte
	kubeletClientCert     []byte
	kubeletClientKey      []byte
	aggregationCA         []byte
	aggregationClientCert []byte
	aggregationClientKey  []byte
	serviceAccountPrivKey []byte // In PKIX form
	serverCert            []byte
	serverKey             []byte
}

func getPKIApiserverConfig(ctx context.Context, kv clientv3.KV, kpki *pki.KubernetesPKI) (*apiserverConfig, error) {
	var config apiserverConfig

	for _, el := range []struct {
		targetCert *[]byte
		targetKey  *[]byte
		name       pki.KubeCertificateName
	}{
		{&config.idCA, nil, pki.IdCA},
		{&config.kubeletClientCert, &config.kubeletClientKey, pki.KubeletClient},
		{&config.aggregationCA, nil, pki.AggregationCA},
		{&config.aggregationClientCert, &config.aggregationClientKey, pki.FrontProxyClient},
		{&config.serverCert, &config.serverKey, pki.APIServer},
	} {
		cert, key, err := kpki.Certificate(ctx, el.name, kv)
		if err != nil {
			return nil, fmt.Errorf("could not load certificate %q from PKI: %w", el.name, err)
		}
		if el.targetCert != nil {
			*el.targetCert = cert
		}
		if el.targetKey != nil {
			*el.targetKey = key
		}
	}

	var err error
	config.serviceAccountPrivKey, err = kpki.ServiceAccountKey(ctx, kv)
	if err != nil {
		return nil, fmt.Errorf("could not load serviceaccount privkey: %w", err)
	}
	return &config, nil
}

func runAPIServer(config apiserverConfig, output io.Writer) supervisor.Runnable {
	return func(ctx context.Context) error {
		args, err := fileargs.New()
		if err != nil {
			panic(err) // If this fails, something is very wrong. Just crash.
		}
		defer args.Close()
		cmd := exec.CommandContext(ctx, "/kubernetes/bin/kube", "kube-apiserver",
			fmt.Sprintf("--advertise-address=%v", config.advertiseAddress.String()),
			"--authorization-mode=Node,RBAC",
			args.FileOpt("--client-ca-file", "client-ca.pem",
				pem.EncodeToMemory(&pem.Block{Type: "CERTIFICATE", Bytes: config.idCA})),
			"--enable-admission-plugins=NodeRestriction,PodSecurityPolicy",
			"--enable-aggregator-routing=true",
			"--insecure-port=0",
			fmt.Sprintf("--secure-port=%v", common.KubernetesAPIPort),
			// Due to the magic of GRPC this really needs four slashes and a :0
			fmt.Sprintf("--etcd-servers=%v", "unix:////consensus/listener.sock:0"),
			args.FileOpt("--kubelet-client-certificate", "kubelet-client-cert.pem",
				pem.EncodeToMemory(&pem.Block{Type: "CERTIFICATE", Bytes: config.kubeletClientCert})),
			args.FileOpt("--kubelet-client-key", "kubelet-client-key.pem",
				pem.EncodeToMemory(&pem.Block{Type: "PRIVATE KEY", Bytes: config.kubeletClientKey})),
			"--kubelet-preferred-address-types=InternalIP",
			args.FileOpt("--proxy-client-cert-file", "aggregation-client-cert.pem",
				pem.EncodeToMemory(&pem.Block{Type: "CERTIFICATE", Bytes: config.aggregationClientCert})),
			args.FileOpt("--proxy-client-key-file", "aggregation-client-key.pem",
				pem.EncodeToMemory(&pem.Block{Type: "PRIVATE KEY", Bytes: config.aggregationClientKey})),
			"--requestheader-allowed-names=front-proxy-client",
			args.FileOpt("--requestheader-client-ca-file", "aggregation-ca.pem",
				pem.EncodeToMemory(&pem.Block{Type: "CERTIFICATE", Bytes: config.aggregationCA})),
			"--requestheader-extra-headers-prefix=X-Remote-Extra-",
			"--requestheader-group-headers=X-Remote-Group",
			"--requestheader-username-headers=X-Remote-User",
			args.FileOpt("--service-account-key-file", "service-account-pubkey.pem",
				pem.EncodeToMemory(&pem.Block{Type: "PRIVATE KEY", Bytes: config.serviceAccountPrivKey})),
			fmt.Sprintf("--service-cluster-ip-range=%v", config.serviceIPRange.String()),
			args.FileOpt("--tls-cert-file", "server-cert.pem",
				pem.EncodeToMemory(&pem.Block{Type: "CERTIFICATE", Bytes: config.serverCert})),
			args.FileOpt("--tls-private-key-file", "server-key.pem",
				pem.EncodeToMemory(&pem.Block{Type: "PRIVATE KEY", Bytes: config.serverKey})),
		)
		if args.Error() != nil {
			return err
		}
		cmd.Stdout = output
		cmd.Stderr = output
		supervisor.Signal(ctx, supervisor.SignalHealthy)
		err = cmd.Run()
		fmt.Fprintf(output, "apiserver stopped: %v\n", err)
		return err
	}
}