Question

I have a structure like this

-------------
|Supervisor |
-------------
      |
-------------
|  Child1   |
-------------
      |
-------------
|  Child2   |
-------------

In this structure, child1 is supervised and it spawns child2. What I need is to be able to restart child1 when child2 crashes/exits. Which would be the best way to achieve this?

Answer 1

If you allow Child1 to crash when Child2 crashes, your existing supervisor
will simply restart Child1, thus also restarting Child2.

But that depends upon Child1 crashing when Child2 crashes. Another option
is to insert another supervisor in the process tree:

Change this:                          Into this:

+------------+                      +------------+
| Supervisor |                      | Supervisor |
+------------+                      +------------+
      |                                   |
+------------+                      +------------+
|   Child1   |  New supervisor ---> | Supervisor |
+------------+                      +------------+
      |                               |      |
+------------+              +------------+ +---------+
|   Child2   |              |   Child1   | |  Child2 |
+------------+              +------------+ +---------+
      |                                        |
 other service                            other service

The new supervisor handles just the two children as their own service, allowing
the death of either one to influence the other in configurable ways.