Added note on tag formatting of docker image (docker#3207)

FrenchBen · Misty Stanley-Jones · commit fe0620225d11 · 2017-05-09T13:02:24.000-07:00
* Added note on tag formatting of docker image

Signed-off-by: French Ben &lt;frenchben@docker.com&gt;

* Updated notes

Signed-off-by: French Ben &lt;frenchben@docker.com&gt;
diff --git a/engine/admin/logging/awslogs.md b/engine/admin/logging/awslogs.md
@@ -74,7 +74,7 @@ $ docker run --log-driver=awslogs \
              ...
 ```
 
-> **Note:**
+> **Note**:
 > Your AWS IAM policy must include the `logs:CreateLogGroup` permission before you attempt to use `awslogs-create-group`.
 
 
@@ -87,6 +87,14 @@ When both `awslogs-stream` and `tag` are specified, the value supplied for `awsl
 
 If not specified, the container ID is used as the log stream.
 
+{% raw %}
+> **Note**:
+> The CloudWatch log API doesn't support `:` in the log name. This can cause some issues when using the `{{ .ImageName }}` as a tag, since a docker image has a format of `IMAGE:TAG`, such as `alpine:latest`.
+> Template markup can be used to get the proper format. 
+> To get the image name and the first 12 characters of the container id, you can use: `--log-opt tag='{{ with split .ImageName ":" }}{{join . "_"}}{{end}}-{{.ID}}'`
+> the output will be something like: `alpine_latest-bf0072049c76` 
+{% endraw %}
+
 
 ## Credentials
 
