Add documentation and changelog entry

CHANGELOG.md

@@ -42,6 +42,7 @@ BUG FIXES:
   * client: Drivers log during fingerprinting [GH-2337]
   * client: Fix race condition with deriving vault tokens [GH-2275]
   * client: Fix remounting alloc dirs after reboots [GH-2391] [GH-2394]
+  * client: Replace `-` with `_` in environment variable names [GH-2406]
   * client: Fix panic and deadlock during client restore state when prestart
     fails [GH-2376] 
   * config: Fix Consul Config Merging/Copying [GH-2278]

website/source/docs/runtime/environment.html.md

@@ -72,6 +72,10 @@ environment variables.
     <td>`NOMAD_ADDR_<label>`</td>
     <td>The IP:Port pair of the port with the given label</td>
   </tr>
+  <tr>
+    <td>`NOMAD_ADDR_<task>_<label`></td>
+    <td>The allocated address, given as IP:Port for the given label of other tasks in the same group</td>
+  </tr>
   <tr>
     <td>`NOMAD_HOST_PORT_<label>`</td>
     <td>The host port for the given label if the port is port mapped</td>
@@ -84,12 +88,12 @@ environment variables.
     <td>`VAULT_TOKEN`</td>
     <td>The task's Vault token. See [Vault Integration](/docs/vault-integration/index.html) for more details</td>
   </tr>
-  <tr>
-    <td>`NOMAD_ADDR_<task>_<label`></td>
-    <td>The allocated address, given as IP:Port, for each task, port label</td>
-  </tr>
 </table>
 
+Port labels and task names will have any dashes `-` in their names replaced by
+underscores `_` when they're used in environment variable names such as
+`NOMAD_ADDR_<task>_<label>`.
+
 ## Task Identifiers
 
 Nomad will pass both the allocation ID and name as well as the task and job's