fix: Add reaper to coder agent (#2441)

* fix: Add reaper to coder agent

- The coder agent runs as PID 1 in some of our Docker workspaces.
  In such cases it is the responsibility of the init process to
  reap dead processes. Failing to do so can result in an inability
  to create new processes by running out of PIDs.

  This PR adds a reaper to our agent that is only spawned if it
  detects that it is PID1.

cli/agent.go

@@ -8,6 +8,7 @@ import (
 	"net/url"
 	"os"
 	"path/filepath"
+	"runtime"
 	"time"
 
 	"cloud.google.com/go/compute/metadata"
@@ -18,6 +19,7 @@ import (
 	"cdr.dev/slog/sloggers/sloghuman"
 
 	"github.com/coder/coder/agent"
+	"github.com/coder/coder/agent/reaper"
 	"github.com/coder/coder/cli/cliflag"
 	"github.com/coder/coder/codersdk"
 	"github.com/coder/retry"
@@ -51,6 +53,23 @@ func workspaceAgent() *cobra.Command {
 			}
 			defer logWriter.Close()
 			logger := slog.Make(sloghuman.Sink(cmd.ErrOrStderr()), sloghuman.Sink(logWriter)).Leveled(slog.LevelDebug)
+
+			isLinux := runtime.GOOS == "linux"
+
+			// Spawn a reaper so that we don't accumulate a ton
+			// of zombie processes.
+			if reaper.IsInitProcess() && !reaper.IsChild() && isLinux {
+				logger.Info(cmd.Context(), "spawning reaper process")
+				err := reaper.ForkReap(nil)
+				if err != nil {
+					logger.Error(cmd.Context(), "failed to reap", slog.Error(err))
+					return xerrors.Errorf("fork reap: %w", err)
+				}
+
+				logger.Info(cmd.Context(), "reaper process exiting")
+				return nil
+			}
+
 			client := codersdk.New(coderURL)
 
 			if pprofEnabled {