Add driver.docker.bridge_ip node attribute

CHANGELOG.md

@@ -28,6 +28,7 @@ IMPROVEMENTS:
  * driver/docker: Allow setting seccomp profiles [GH-2658]
  * driver/docker: Support Docker credential helpers [GH-2651]
  * driver/docker: Auth failures can optionally be ignored [GH-2786]
+ * driver/docker: Add `driver.docker.bridge_ip` node attribute [GH-2797]
  * driver/docker: Allow setting container IP with user defined networks
    [GH-2535]
  * driver/rkt: Support `no_overlay` [GH-2702]

client/driver/docker.go

@@ -319,6 +319,9 @@ func (d *DockerDriver) Fingerprint(cfg *config.Config, node *structs.Node) (bool
 		d.fingerprintSuccess = helper.BoolToPtr(false)
 		return false, nil
 	}
+	for i, v := range *env {
+		d.logger.Printf("[DEBUG] driver.docker: %d %s", i, v)
+	}
 
 	node.Attributes[dockerDriverAttr] = "1"
 	node.Attributes["driver.docker.version"] = env.Get("Version")
@@ -333,6 +336,24 @@ func (d *DockerDriver) Fingerprint(cfg *config.Config, node *structs.Node) (bool
 		node.Attributes["driver."+dockerVolumesConfigOption] = "1"
 	}
 
+	// Detect bridge IP address - #2785
+	if nets, err := client.ListNetworks(); err != nil {
+		d.logger.Printf("[WARN] driver.docker: error discovering bridge IP: %v", err)
+	} else {
+		for _, n := range nets {
+			if n.Name != "bridge" {
+				continue
+			}
+
+			if len(n.IPAM.Config) == 0 {
+				d.logger.Printf("[WARN] driver.docker: no IPAM config for bridge network")
+				break
+			}
+
+			node.Attributes["driver.docker.bridge_ip"] = n.IPAM.Config[0].Gateway
+		}
+	}
+
 	d.fingerprintSuccess = helper.BoolToPtr(true)
 	return true, nil
 }

client/driver/docker_test.go

@@ -15,6 +15,7 @@ import (
 	"time"
 
 	docker "github.com/fsouza/go-dockerclient"
+	sockaddr "github.com/hashicorp/go-sockaddr"
 	"github.com/hashicorp/nomad/client/allocdir"
 	"github.com/hashicorp/nomad/client/config"
 	"github.com/hashicorp/nomad/client/driver/env"
@@ -177,6 +178,40 @@ func TestDockerDriver_Fingerprint(t *testing.T) {
 	t.Logf("Found docker version %s", node.Attributes["driver.docker.version"])
 }
 
+// TestDockerDriver_Fingerprint_Bridge asserts that if Docker is running we set
+// the bridge network's IP as a node attribute. See #2785
+func TestDockerDriver_Fingerprint_Bridge(t *testing.T) {
+	if !testutil.DockerIsConnected(t) {
+		t.Skip("requires Docker")
+	}
+
+	// This seems fragile, so we might need to reconsider this test if it
+	// proves flaky
+	expectedAddr, err := sockaddr.GetInterfaceIP("docker0")
+	if err != nil {
+		t.Fatalf("unable to get ip for docker0: %v", err)
+	}
+	if expectedAddr == "" {
+		t.Fatalf("unable to get ip for docker bridge")
+	}
+
+	conf := testConfig()
+	conf.Node = mock.Node()
+	dd := NewDockerDriver(NewDriverContext("", "", conf, conf.Node, testLogger(), nil))
+	ok, err := dd.Fingerprint(conf, conf.Node)
+	if err != nil {
+		t.Fatalf("error fingerprinting docker: %v", err)
+	}
+	if !ok {
+		t.Fatalf("expected Docker to be enabled but false was returned")
+	}
+
+	if found := conf.Node.Attributes["driver.docker.bridge_ip"]; found != expectedAddr {
+		t.Fatalf("expected bridge ip %q but found: %q", expectedAddr, found)
+	}
+	t.Logf("docker bridge ip: %q", conf.Node.Attributes["driver.docker.bridge_ip"])
+}
+
 func TestDockerDriver_StartOpen_Wait(t *testing.T) {
 	if !testutil.DockerIsConnected(t) {
 		t.SkipNow()

website/source/docs/drivers/docker.html.md

@@ -529,6 +529,8 @@ The `docker` driver will set the following client attributes:
 
 * `driver.docker` - This will be set to "1", indicating the driver is
   available.
+* `driver.docker.bridge_ip` - The IP of the Docker bridge network if one
+  exists.
 * `driver.docker.version` - This will be set to version of the docker server.
 
 Here is an example of using these properties in a job file: