feat: Add logging options for coder agent (#7474)

Similar to logging options in the coderd server, but for the agent
running in workspaces. Meant to make hollistic log collection and
querying simpler.

cli/agent.go

@@ -22,6 +22,8 @@ import (
 
 	"cdr.dev/slog"
 	"cdr.dev/slog/sloggers/sloghuman"
+	"cdr.dev/slog/sloggers/slogjson"
+	"cdr.dev/slog/sloggers/slogstackdriver"
 	"github.com/coder/coder/agent"
 	"github.com/coder/coder/agent/reaper"
 	"github.com/coder/coder/buildinfo"
@@ -40,6 +42,9 @@ func (r *RootCmd) workspaceAgent() *clibase.Cmd {
 		tailnetListenPort   int64
 		prometheusAddress   string
 		debugAddress        string
+		slogHumanPath       string
+		slogJSONPath        string
+		slogStackdriverPath string
 	)
 	cmd := &clibase.Cmd{
 		Use:   "agent",
@@ -62,7 +67,46 @@ func (r *RootCmd) workspaceAgent() *clibase.Cmd {
 					MaxSize:  5, // MB
 				}
 				defer logWriter.Close()
-				logger := slog.Make(sloghuman.Sink(inv.Stderr), sloghuman.Sink(logWriter)).Leveled(slog.LevelDebug)
+
+				sinks := []slog.Sink{sloghuman.Sink(logWriter)}
+				closers := []func() error{}
+				addSinkIfProvided := func(sinkFn func(io.Writer) slog.Sink, loc string) error {
+					switch loc {
+					case "":
+
+					case "/dev/stdout":
+						sinks = append(sinks, sinkFn(inv.Stdout))
+
+					case "/dev/stderr":
+						sinks = append(sinks, sinkFn(inv.Stderr))
+
+					default:
+						fi, err := os.OpenFile(loc, os.O_WRONLY|os.O_CREATE|os.O_APPEND, 0o644)
+						if err != nil {
+							return xerrors.Errorf("open log file %q: %w", loc, err)
+						}
+						closers = append(closers, fi.Close)
+						sinks = append(sinks, sinkFn(fi))
+					}
+					return nil
+				}
+
+				if err := addSinkIfProvided(sloghuman.Sink, slogHumanPath); err != nil {
+					return xerrors.Errorf("add human sink: %w", err)
+				}
+				if err := addSinkIfProvided(slogjson.Sink, slogJSONPath); err != nil {
+					return xerrors.Errorf("add json sink: %w", err)
+				}
+				if err := addSinkIfProvided(slogstackdriver.Sink, slogStackdriverPath); err != nil {
+					return xerrors.Errorf("add stackdriver sink: %w", err)
+				}
+
+				logger := slog.Make(sinks...).Leveled(slog.LevelDebug)
+				defer func() {
+					for _, closer := range closers {
+						_ = closer()
+					}
+				}()
 
 				logger.Info(ctx, "spawning reaper process")
 				// Do not start a reaper on the child process. It's important
@@ -290,6 +334,30 @@ func (r *RootCmd) workspaceAgent() *clibase.Cmd {
 			Value:       clibase.StringOf(&debugAddress),
 			Description: "The bind address to serve a debug HTTP server.",
 		},
+		{
+			Name:        "Human Log Location",
+			Description: "Output human-readable logs to a given file.",
+			Flag:        "log-human",
+			Env:         "CODER_AGENT_LOGGING_HUMAN",
+			Default:     "/dev/stderr",
+			Value:       clibase.StringOf(&slogHumanPath),
+		},
+		{
+			Name:        "JSON Log Location",
+			Description: "Output JSON logs to a given file.",
+			Flag:        "log-json",
+			Env:         "CODER_AGENT_LOGGING_JSON",
+			Default:     "",
+			Value:       clibase.StringOf(&slogJSONPath),
+		},
+		{
+			Name:        "Stackdriver Log Location",
+			Description: "Output Stackdriver compatible logs to a given file.",
+			Flag:        "log-stackdriver",
+			Env:         "CODER_AGENT_LOGGING_STACKDRIVER",
+			Default:     "",
+			Value:       clibase.StringOf(&slogStackdriverPath),
+		},
 	}
 
 	return cmd

cli/testdata/coder_agent_--help.golden

@@ -3,6 +3,15 @@ Usage: coder agent [flags]
 Starts the Coder workspace agent.
 
 Options
+      --log-human string, $CODER_AGENT_LOGGING_HUMAN (default: /dev/stderr)
+          Output human-readable logs to a given file.
+
+      --log-json string, $CODER_AGENT_LOGGING_JSON
+          Output JSON logs to a given file.
+
+      --log-stackdriver string, $CODER_AGENT_LOGGING_STACKDRIVER
+          Output Stackdriver compatible logs to a given file.
+
       --auth string, $CODER_AGENT_AUTH (default: token)
           Specify the authentication type to use for the agent.