tr: expose envoy sidecar admin port as environment variable

client/allocrunner/taskrunner/envoybootstrap_hook.go

@@ -13,12 +13,16 @@ import (
 	"github.com/hashicorp/nomad/client/allocdir"
 	"github.com/hashicorp/nomad/client/allocrunner/interfaces"
 	agentconsul "github.com/hashicorp/nomad/command/agent/consul"
+	"github.com/hashicorp/nomad/helper"
 	"github.com/hashicorp/nomad/nomad/structs"
 )
 
 var _ interfaces.TaskPrestartHook = &envoyBootstrapHook{}
 
-const envoyBaseAdminPort = 19000
+const (
+	envoyBaseAdminPort      = 19000
+	envoyAdminBindEnvPrefix = "NOMAD_ENVOY_ADMIN_ADDR_"
+)
 
 // envoyBootstrapHook writes the bootstrap config for the Connect Envoy proxy
 // sidecar.
@@ -82,6 +86,7 @@ func (h *envoyBootstrapHook) Prestart(ctx context.Context, req *interfaces.TaskP
 	// are running, the bind addresses need to have unique ports.
 	// TODO: support running in host netns, using freeport to find available port
 	envoyAdminBind := buildEnvoyAdminBind(h.alloc, req.Task.Name)
+	resp.Env[helper.CleanEnvVar(envoyAdminBindEnvPrefix+serviceName, '_')] = envoyAdminBind
 
 	// Envoy bootstrap configuration may contain a Consul token, so write
 	// it to the secrets directory like Vault tokens.

website/source/docs/runtime/_envvars.html.md.erb

@@ -161,4 +161,11 @@
       Consul Connect <a href="/docs/job-specification/upstreams.html">upstream</a>. 
     </td>
   </tr>
+  <tr>
+    <td><tt>NOMAD&lowbar;ENVOY&lowbar;ADMIN&lowbar;ADDR&lowbar;&lt;service&gt;</tt></td>
+    <td>
+      Local address <tt>localhost:Port</tt> for the admin port of the envoy sidecar for the
+      given <tt>service</tt> when defined as a Consul Connect enabled service. 
+    </td>
+  </tr>
 </table>