api: add Hostname, ExtraHosts for pause container

This change adds Hostname and ExtraHosts to the pause container's docker
config and host config respectively. This allows awsvpc tasks to have
/etc/hosts entries for the ENI private ips

agent/api/eni.go

@@ -60,6 +60,14 @@ func (eni *ENI) GetIPV6Addresses() []string {
 	return addresses
 }
 
+// GetHostname returns the hostname assigned to the ENI
+func (eni *ENI) GetHostname() string {
+	// WIP
+	// pending acs model change to include hostname
+	// return eni.Hostname
+	return "ip.region.compute.internal"
+}
+
 // String returns a human readable version of the ENI object
 func (eni *ENI) String() string {
 	var ipv4Addresses []string

agent/api/task.go

@@ -473,6 +473,12 @@ func (task *Task) dockerConfig(container *Container, apiVersion dockerclient.Doc
 		config.Labels = make(map[string]string)
 	}
 
+	if container.Type == ContainerCNIPause {
+		// WIP
+		// hostname to pause container's docker config
+		return task.applyENIHostname(config), nil
+	}
+
 	return config, nil
 }
 
@@ -625,6 +631,13 @@ func (task *Task) dockerHostConfig(container *Container, dockerContainerMap map[
 	hostConfig.NetworkMode = networkMode
 	// Override 'awsvpc' parameters if needed
 	if container.Type == ContainerCNIPause {
+
+		// WIP
+		// apply ExtraHosts to HostConfig for pause container
+		if hosts := task.generateENIExtraHosts(); hosts != nil {
+			hostConfig.ExtraHosts = append(hostConfig.ExtraHosts, hosts...)
+		}
+
 		// Override the DNS settings for the pause container if ENI has custom
 		// DNS settings
 		return task.overrideDNS(hostConfig), nil
@@ -695,6 +708,46 @@ func (task *Task) overrideDNS(hostConfig *docker.HostConfig) *docker.HostConfig
 	return hostConfig
 }
 
+// applyENIHostname adds the hostname provided by the ENI message to the
+// container's docker config. At the time of implmentation, we are only using it
+// to configure the pause container for awsvpc tasks
+func (task *Task) applyENIHostname(dockerConfig *docker.Config) *docker.Config {
+	eni := task.GetTaskENI()
+	if eni == nil {
+		return dockerConfig
+	}
+
+	hostname := eni.GetHostname()
+	if hostname == "" {
+		return dockerConfig
+	}
+
+	dockerConfig.Hostname = hostname
+	return dockerConfig
+}
+
+// generateENIExtraHosts returns a slice of strings of the form "hostname:ip"
+// that is generated using the hostname and ip addresses allocated to the ENI
+func (task *Task) generateENIExtraHosts() []string {
+	eni := task.GetTaskENI()
+	if eni == nil {
+		return nil
+	}
+
+	hostname := eni.GetHostname()
+	if hostname == "" {
+		return nil
+	}
+
+	extraHosts := []string{}
+
+	for _, ip := range eni.GetIPV6Addresses() {
+		host := fmt.Sprintf("%s:%s", hostname, ip)
+		extraHosts = append(extraHosts, host)
+	}
+	return extraHosts
+}
+
 func (task *Task) dockerLinks(container *Container, dockerContainerMap map[string]*DockerContainer) ([]string, error) {
 	dockerLinkArr := make([]string, len(container.Links))
 	for i, link := range container.Links {

agent/api/task_test.go

@@ -281,6 +281,9 @@ func TestDockerHostConfigPauseContainer(t *testing.T) {
 	assert.Nil(t, err)
 	assert.Equal(t, []string{"169.254.169.253"}, config.DNS)
 	assert.Equal(t, []string{"us-west-2.compute.internal"}, config.DNSSearch)
+
+	// Verify ExtraHosts are added for eni IPs
+
 }
 
 func TestBadDockerHostConfigRawConfig(t *testing.T) {