@@ -271,15 +271,16 @@ func (b *Builder) build(stdout io.Writer, stderr io.Writer, out io.Writer) (stri

 	}

 	// check if there are any leftover build-args that were passed but not

-	// consumed during build. Return an error, if there are any.

+	// consumed during build. Return a warning, if there are any.

 	leftoverArgs := []string{}

 	for arg := range b.options.BuildArgs {

 		if !b.isBuildArgAllowed(arg) {

 			leftoverArgs = append(leftoverArgs, arg)

 		}

 	}

+

 	if len(leftoverArgs) > 0 {

-		return "", fmt.Errorf("One or more build-args %v were not consumed, failing build.", leftoverArgs)

+		fmt.Fprintf(b.Stderr, "[Warning] One or more build-args %v were not consumed\n", leftoverArgs)

 	}

 	if b.image == "" {

@@ -1286,12 +1286,12 @@ to create the directory in the Dockerfile. For example:

     ARG <name>[=<default value>]

 The `ARG` instruction defines a variable that users can pass at build-time to

-the builder with the `docker build` command using the

-`--build-arg <varname>=<value>` flag. If a user specifies a build argument

-that was not defined in the Dockerfile, the build outputs an error.

+the builder with the `docker build` command using the `--build-arg

+<varname>=<value>` flag. If a user specifies a build argument that was not

+defined in the Dockerfile, the build outputs a warning.

 ```

-One or more build-args were not consumed, failing build.

+[Warning] One or more build-args [foo] were not consumed.

 ```

 The Dockerfile author can define a single variable by specifying `ARG` once or many

@@ -6056,11 +6056,12 @@ func (s *DockerSuite) TestBuildBuildTimeArgUnconsumedArg(c *check.C) {

 		RUN echo $%s

 		CMD echo $%s`, envKey, envKey)

-	errStr := "One or more build-args"

-	if _, out, err := buildImageWithOut(imgName, dockerfile, true, args...); err == nil {

-		c.Fatalf("build succeeded, expected to fail. Output: %v", out)

-	} else if !strings.Contains(out, errStr) {

-		c.Fatalf("Unexpected error. output: %q, expected error: %q", out, errStr)

+	warnStr := "[Warning] One or more build-args"

+

+	if _, out, err := buildImageWithOut(imgName, dockerfile, true, args...); !strings.Contains(out, warnStr) {

+		c.Fatalf("build completed without warning: %q %q", out, err)

+	} else if err != nil {

+		c.Fatalf("build failed to complete: %q %q", out, err)

 	}

 }

@@ -26,7 +26,7 @@ For example:

 # DESCRIPTION

-A Dockerfile is a file that automates the steps of creating a Docker image. 

+A Dockerfile is a file that automates the steps of creating a Docker image.

 A Dockerfile is similar to a Makefile.

 # USAGE

@@ -71,10 +71,10 @@ A Dockerfile is similar to a Makefile.

   multiple images. Make a note of the last image ID output by the commit before

   each new **FROM** command.

-  -- If no tag is given to the **FROM** instruction, Docker applies the 

+  -- If no tag is given to the **FROM** instruction, Docker applies the

   `latest` tag. If the used tag does not exist, an error is returned.

-  -- If no digest is given to the **FROM** instruction, Docker applies the 

+  -- If no digest is given to the **FROM** instruction, Docker applies the

   `latest` tag. If the used tag does not exist, an error is returned.

 **MAINTAINER**

@@ -148,7 +148,7 @@ A Dockerfile is similar to a Makefile.

   ```

   -- To make the container run the same executable every time, use **ENTRYPOINT** in

-  combination with **CMD**. 

+  combination with **CMD**.

   If the user specifies arguments to `docker run`, the specified commands

   override the default in **CMD**.

   Do not confuse **RUN** with **CMD**. **RUN** runs a command and commits the result.

@@ -156,7 +156,7 @@ A Dockerfile is similar to a Makefile.

   the image.

 **LABEL**

-  -- `LABEL <key>=<value> [<key>=<value> ...]`or 

+  -- `LABEL <key>=<value> [<key>=<value> ...]`or

   ```

   LABEL <key>[ <value>]

   LABEL <key>[ <value>]

@@ -176,8 +176,8 @@ A Dockerfile is similar to a Makefile.

   ```

   An image can have more than one label. To specify multiple labels, separate

-  each key-value pair by a space. 

-  

+  each key-value pair by a space.

+

   Labels are additive including `LABEL`s in `FROM` images. As the system

   encounters and then applies a new label, new `key`s override any previous

   labels with identical keys.

@@ -194,7 +194,7 @@ A Dockerfile is similar to a Makefile.

 **ENV**

   -- `ENV <key> <value>`

   The **ENV** instruction sets the environment variable <key> to

-  the value `<value>`. This value is passed to all future 

+  the value `<value>`. This value is passed to all future

   **RUN**, **ENTRYPOINT**, and **CMD** instructions. This is

   functionally equivalent to prefixing the command with `<key>=<value>`.  The

   environment variables that are set with **ENV** persist when a container is run

@@ -243,7 +243,7 @@ A Dockerfile is similar to a Makefile.

   being built (the context of the build) or a remote file URL. The `<dest>` is an

   absolute path, or a path relative to **WORKDIR**, into which the source will

   be copied inside the target container. If you **COPY** an archive file it will

-  land in the container exactly as it appears in the build context without any 

+  land in the container exactly as it appears in the build context without any

   attempt to unpack it.  All new files and directories are created with mode **0755**

   and with the uid and gid of **0**.

@@ -326,10 +326,10 @@ A Dockerfile is similar to a Makefile.

   The `ARG` instruction defines a variable that users can pass at build-time to

   the builder with the `docker build` command using the `--build-arg

   <varname>=<value>` flag. If a user specifies a build argument that was not

-  defined in the Dockerfile, the build outputs an error.

+  defined in the Dockerfile, the build outputs a warning.

   ```

-  One or more build-args were not consumed, failing build.

+  [Warning] One or more build-args [foo] were not consumed

   ```

   The Dockerfile author can define a single variable by specifying `ARG` once or many

@@ -454,7 +454,7 @@ A Dockerfile is similar to a Makefile.

   you are defining an image to use as a base for building other images. For

   example, if you are defining an application build environment or a daemon that

   is customized with a user-specific configuration.  

-  

+

   Consider an image intended as a reusable python application builder. It must

   add application source code to a particular directory, and might need a build

   script called after that. You can't just call **ADD** and **RUN** now, because

@@ -470,4 +470,5 @@ A Dockerfile is similar to a Makefile.

 # HISTORY

 *May 2014, Compiled by Zac Dover (zdover at redhat dot com) based on docker.com Dockerfile documentation.

 *Feb 2015, updated by Brian Goff (cpuguy83@gmail.com) for readability

-*Sept 2015, updated by Sally O'Malley (somalley@redhat.com) 

+*Sept 2015, updated by Sally O'Malley (somalley@redhat.com)

+*Oct 2016, updated by Addam Hardy (addam.hardy@gmail.com)