config: set recover_stopped to default to false (#260)

The use of recover_stopped may cause the Nomad agent to hang on startup,
as the plugin tries to start an exited podman task. Podman itself will
hang forever in this state, and the http client on the Nomad side is also
unable to timeout in this case. The result is a permenantly hung Nomad
agent, until someone force kills either Nomad or Podman.

Also emit a log warning that recover_stopped should not be used. We leave
it in place for compatability.

Fixes #229

config.go

@@ -4,6 +4,7 @@
 package main
 
 import (
+	"github.com/hashicorp/go-hclog"
 	"github.com/hashicorp/nomad/helper/pluginutils/hclutils"
 	"github.com/hashicorp/nomad/plugins/shared/hclspec"
 )
@@ -33,7 +34,7 @@ var (
 		// allow TaskRecover to start a still existing, stopped, container during client/driver restart
 		"recover_stopped": hclspec.NewDefault(
 			hclspec.NewAttr("recover_stopped", "bool", false),
-			hclspec.NewLiteral("true"),
+			hclspec.NewLiteral("false"),
 		),
 		// optional extra_labels to append to all tasks for observability. Globs supported
 		"extra_labels": hclspec.NewAttr("extra_labels", "list(string)", false),
@@ -130,6 +131,13 @@ type PluginConfig struct {
 	ExtraLabels          []string     `codec:"extra_labels"`
 }
 
+// LogWarnings will emit logs about known problematic configurations
+func (c *PluginConfig) LogWarnings(logger hclog.Logger) {
+	if c.RecoverStopped {
+		logger.Error("WARNING - use of recover_stopped may cause Nomad agent to not start on system restarts")
+	}
+}
+
 // TaskConfig is the driver configuration of a task within a job
 type TaskConfig struct {
 	ApparmorProfile   string             `codec:"apparmor_profile"`

driver.go

@@ -225,6 +225,9 @@ func (d *Driver) Capabilities() (*drivers.Capabilities, error) {
 // then send periodic updates at an interval that is appropriate for the driver
 // until the context is canceled.
 func (d *Driver) Fingerprint(ctx context.Context) (<-chan *drivers.Fingerprint, error) {
+	// emit warnings about known bad configs
+	d.config.LogWarnings(d.logger)
+
 	err := shelpers.Init()
 	if err != nil {
 		d.logger.Error("Could not init stats helper", "error", err)