Add an autostart, for autoloading from the "ssh_private_key" env var.

Dockerfile

@@ -9,7 +9,7 @@ RUN rm -rf /var/cache/apk/*
 RUN mkdir ~/.ssh
 
 # Copy in our executables.
-COPY agent-start agent-stop agent-add /bin/
+COPY agent-start agent-stop agent-add agent-autostart /bin/
 COPY hosts-clear hosts-add /bin/
 RUN chmod +x /bin/agent-* /bin/hosts-*
 

agent-autostart

@@ -0,0 +1,4 @@
+#!/bin/sh
+
+source agent-start
+echo "$SSH_PRIVATE_KEY" | agent-add