Switch to a slimmer distroless base image.

At a high level, it switches us to a distroless base container image, but that also includes several related bits:

- Add a writable /tmp but make the rest of our filesystems read-only at runtime.

- Condense our main server binaries into a single pinniped-server binary. This saves a bunch of space in
  the image due to duplicated library code. The correct behavior is dispatched based on `os.Args[0]`, and
  the `pinniped-server` binary is symlinked to `pinniped-concierge` and `pinniped-supervisor`.

- Strip debug symbols from our binaries. These aren't really useful in a distroless image anyway and all the
  normal stuff you'd expect to work, such as stack traces, still does.

- Add a separate `pinniped-concierge-kube-cert-agent` binary with "sleep" and "print" functionality instead of
  using builtin /bin/sleep and /bin/cat for the kube-cert-agent. This is split from the main server binary
  because the loading/init time of the main server binary was too large for the tiny resource footprint we
  established in our kube-cert-agent PodSpec. Using a separate binary eliminates this issue and the extra
  binary adds only around 1.5MiB of image size.

- Switch the kube-cert-agent code to use a JSON `{"tls.crt": "<b64 cert>", "tls.key": "<b64 key>"}` format.
  This is more robust to unexpected input formatting than the old code, which simply concatenated the files
  with some extra newlines and split on whitespace.

- Update integration tests that made now-invalid assumptions about the `pinniped-server` image.

Signed-off-by: Matt Moyer <moyerm@vmware.com>

cmd/pinniped-concierge-kube-cert-agent/main.go

@@ -0,0 +1,55 @@
+// Copyright 2021 the Pinniped contributors. All Rights Reserved.
+// SPDX-License-Identifier: Apache-2.0
+
+// Package main is the combined entrypoint for the Pinniped "kube-cert-agent" component.
+package main
+
+import (
+	"encoding/base64"
+	"encoding/json"
+	"io"
+	"io/ioutil"
+	"log"
+	"math"
+	"os"
+	"time"
+)
+
+//nolint: gochecknoglobals // these are swapped during unit tests.
+var (
+	getenv = os.Getenv
+	fail   = log.Fatalf
+	sleep  = time.Sleep
+	out    = io.Writer(os.Stdout)
+)
+
+func main() {
+	if len(os.Args) < 2 {
+		fail("missing subcommand")
+	}
+
+	switch os.Args[1] {
+	case "sleep":
+		sleep(math.MaxInt64)
+	case "print":
+		certBytes, err := ioutil.ReadFile(getenv("CERT_PATH"))
+		if err != nil {
+			fail("could not read CERT_PATH: %v", err)
+		}
+		keyBytes, err := ioutil.ReadFile(getenv("KEY_PATH"))
+		if err != nil {
+			fail("could not read KEY_PATH: %v", err)
+		}
+		if err := json.NewEncoder(out).Encode(&struct {
+			Cert string `json:"tls.crt"`
+			Key  string `json:"tls.key"`
+		}{
+			Cert: base64.StdEncoding.EncodeToString(certBytes),
+			Key:  base64.StdEncoding.EncodeToString(keyBytes),
+		}); err != nil {
+			fail("failed to write output: %v", err)
+		}
+	default:
+		fail("invalid subcommand %q", os.Args[1])
+	}
+}

cmd/pinniped-concierge-kube-cert-agent/main_test.go

@@ -0,0 +1,128 @@
+// Copyright 2021 the Pinniped contributors. All Rights Reserved.
+// SPDX-License-Identifier: Apache-2.0
+
+package main
+
+import (
+	"bytes"
+	"fmt"
+	"log"
+	"os"
+	"testing"
+	"time"
+
+	"github.com/stretchr/testify/require"
+)
+
+type errWriter struct{}
+
+func (e errWriter) Write([]byte) (int, error) { return 0, fmt.Errorf("some write error") }
+
+func TestEntrypoint(t *testing.T) {
+	for _, tt := range []struct {
+		name        string
+		args        []string
+		env         map[string]string
+		failOutput  bool
+		wantSleep   time.Duration
+		wantLog     string
+		wantOutJSON string
+		wantFail    bool
+	}{
+		{
+			name:     "missing args",
+			args:     []string{},
+			wantLog:  "missing subcommand\n",
+			wantFail: true,
+		},
+		{
+			name:     "invalid subcommand",
+			args:     []string{"/path/to/binary", "invalid"},
+			wantLog:  "invalid subcommand \"invalid\"\n",
+			wantFail: true,
+		},
+		{
+			name:      "valid sleep",
+			args:      []string{"/path/to/binary", "sleep"},
+			wantSleep: 2562047*time.Hour + 47*time.Minute + 16*time.Second + 854775807*time.Nanosecond, // math.MaxInt64 nanoseconds, approximately 290 years
+		},
+		{
+			name: "missing cert file",
+			args: []string{"/path/to/binary", "print"},
+			env: map[string]string{
+				"CERT_PATH": "./does/not/exist",
+				"KEY_PATH":  "./testdata/test.key",
+			},
+			wantFail: true,
+			wantLog:  "could not read CERT_PATH: open ./does/not/exist: no such file or directory\n",
+		},
+		{
+			name: "missing key file",
+			args: []string{"/path/to/binary", "print"},
+			env: map[string]string{
+				"CERT_PATH": "./testdata/test.crt",
+				"KEY_PATH":  "./does/not/exist",
+			},
+			wantFail: true,
+			wantLog:  "could not read KEY_PATH: open ./does/not/exist: no such file or directory\n",
+		},
+		{
+			name: "fail to write output",
+			args: []string{"/path/to/binary", "print"},
+			env: map[string]string{
+				"CERT_PATH": "./testdata/test.crt",
+				"KEY_PATH":  "./testdata/test.key",
+			},
+			failOutput: true,
+			wantFail:   true,
+			wantLog:    "failed to write output: some write error\n",
+		},
+		{
+			name: "successful print",
+			args: []string{"/path/to/binary", "print"},
+			env: map[string]string{
+				"CERT_PATH": "./testdata/test.crt",
+				"KEY_PATH":  "./testdata/test.key",
+			},
+			wantOutJSON: `{
+				"tls.crt": "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",
+				"tls.key": "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"
+			}`,
+		},
+	} {
+		tt := tt
+		t.Run(tt.name, func(t *testing.T) {
+			var logBuf bytes.Buffer
+			testLog := log.New(&logBuf, "", 0)
+			exited := "exiting via fatal"
+			fail = func(format string, v ...interface{}) {
+				testLog.Printf(format, v...)
+				panic(exited)
+			}
+
+			var sawSleep time.Duration
+			sleep = func(d time.Duration) { sawSleep = d }
+
+			var sawOutput bytes.Buffer
+			out = &sawOutput
+			if tt.failOutput {
+				out = &errWriter{}
+			}
+
+			os.Args = tt.args
+			getenv = func(key string) string { return tt.env[key] }
+			if tt.wantFail {
+				require.PanicsWithValue(t, exited, main)
+			} else {
+				require.NotPanics(t, main)
+			}
+			require.Equal(t, tt.wantSleep.String(), sawSleep.String())
+			require.Equal(t, tt.wantLog, logBuf.String())
+			if tt.wantOutJSON == "" {
+				require.Empty(t, sawOutput.String())
+			} else {
+				require.JSONEq(t, tt.wantOutJSON, sawOutput.String())
+			}
+		})
+	}
+}

cmd/pinniped-concierge-kube-cert-agent/testdata/test.crt

@@ -0,0 +1,17 @@
+-----BEGIN CERTIFICATE-----
+MIICyDCCAbCgAwIBAgIBADANBgkqhkiG9w0BAQsFADAVMRMwEQYDVQQDEwprdWJl
+cm5ldGVzMB4XDTIwMDcyNTIxMDQxOFoXDTMwMDcyMzIxMDQxOFowFTETMBEGA1UE
+AxMKa3ViZXJuZXRlczCCASIwDQYJKoZIhvcNAQEBBQADggEPADCCAQoCggEBAL3K
+hYv2gIQ1Dwzh2cWMid+ofAnvLIfV2Xv61vTLGprUI+XUqB4/gtf6X6UNn0Lett2n
+d8p4wy7hw73hU/ggdvmWJvqBrSjc3JGfy+kj66fKXX+PTlbL7QbwiRvcSqIXIWlV
+lHHxECWrED8jCulw/NVqfook/h5iNUCT9yswSJr/0fImiVnoTlIoEYG2eCNejZ5c
+g39uD3ZTqd9ZxWwSLLnI+2kpJnZBPcd1ZQ8AQqzDgZtYRCqacn5gckQUKZWKQlxo
+Eft6g1XHJouAWAZw7hEtk0v8rG0/eKF7wamxFi6BFVlbjWBsB4T9rApbdBWTKeCJ
+Hv8fv5RMFSzpT3uzTO8CAwEAAaMjMCEwDgYDVR0PAQH/BAQDAgKkMA8GA1UdEwEB
+/wQFMAMBAf8wDQYJKoZIhvcNAQELBQADggEBACh5RhbxqJe+Z/gc17cZhKNmdiwu
+I2pLp3QBfwvN+Wbmajzw/7rYhY0d8JYVTJzXSCPWi6UAKxAtXOLF8WIIf9i39n6R
+uKOBGW14FzzGyRJiD3qaG/JTvEW+SLhwl68Ndr5LHSnbugAqq31abcQy6Zl9v5A8
+JKC97Lj/Sn8rj7opKy4W3oq7NCQsAb0zh4IllRF6UvSnJySfsg7xdXHHpxYDHtOS
+XcOu5ySUIZTgFe9RfeUZlGZ5xn0ckMlQ7qW2Wx1q0OVWw5us4NtkGqKrHG4Tn1X7
+uwo/Yytn5sDxrDv1/oii6AZOCsTPre4oD3wz4nmVzCVJcgrqH4Q24hT8WNg=
+-----END CERTIFICATE-----

cmd/pinniped-concierge-kube-cert-agent/testdata/test.key

@@ -0,0 +1,27 @@
+-----BEGIN RSA PRIVATE KEY-----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+-----END RSA PRIVATE KEY-----