invoker: use locally available image if docker pull fails

core/invoker/src/main/scala/whisk/core/containerpool/docker/DockerClient.scala

@@ -102,6 +102,12 @@ class DockerClient(dockerHost: Option[String] = None)(executionContext: Executio
       runCmd("pull", image).map(_ => ()).andThen { case _ => pullsInFlight.remove(image) }
     })
 
+  def imagePresent(image: String)(implicit transid: TransactionId): Future[String] = {
+    // --format only added to keep the output minimal
+    val cmd = dockerCmd ++ Seq("inspect", "--format={{.Config.Image}}", image)
+    executeProcess(cmd: _*)
+  }
+
   def isOomKilled(id: ContainerId)(implicit transid: TransactionId): Future[Boolean] =
     runCmd("inspect", id.asString, "--format", "{{.State.OOMKilled}}").map(_.toBoolean)
 
@@ -181,6 +187,14 @@ trait DockerApi {
    */
   def pull(image: String)(implicit transid: TransactionId): Future[Unit]
 
+  /**
+   * Checks if image is present locally.
+   *
+   * @param image the image to check
+   * @return a Future completing successful wif the image is present locally, or failing if not
+   */
+  def imagePresent(image: String)(implicit transid: TransactionId): Future[String]
+
   /**
    * Determines whether the given container was killed due to
    * memory constraints.

core/invoker/src/main/scala/whisk/core/containerpool/docker/DockerContainer.scala

@@ -89,7 +89,11 @@ object DockerContainer {
       params
     val pulled = if (userProvidedImage) {
       docker.pull(image).recoverWith {
-        case _ => Future.failed(BlackboxStartupError(s"Failed to pull container image '${image}'."))
+        case _ =>
+          // check if image exists locally and reuse that one
+          docker.imagePresent(image).recoverWith {
+            case _ => Future.failed(BlackboxStartupError(s"Failed to pull container image '${image}'."))
+          }
       }
     } else Future.successful(())
 

tests/src/test/scala/whisk/core/containerpool/docker/test/DockerContainerTests.scala

@@ -681,6 +681,10 @@ class DockerContainerTests
       Future.successful(())
     }
 
+    def imagePresent(image: String)(implicit transid: TransactionId): Future[String] = {
+      Future.failed(new Exception())
+    }
+
     override def isOomKilled(id: ContainerId)(implicit transid: TransactionId): Future[Boolean] = ???
 
     def rawContainerLogs(containerId: ContainerId, fromPos: Long): Future[ByteBuffer] = {