# bond::Bond() and bond id discovery

As far as I can tell, there is no discovery mechanism built in to the bond::Bond node. My use case is that I want to develop a generic Watchdog node that monitors two nodes at either end of a topic (or whatever) like this:

/node/one  <===Bond===> Watchdog <===Bond===> /node/two


So, if /node/one dies, the Watchdog can take some action with /node/two. Hard-coding IDs seems error-prone and awkward for arbitrary connections, so I wonder is there is a simple solution here. Ideally I would want to write a mixin class that I can add to my nodelets with just a single line, and the most obvious solution to me is advertising a well-known service on each node like so:

/node/one                    Watchdog                  /node/two
node1.request("/watchdog/bond", "bond_123456")
Check "bond_123456" OK
return OK (or alternative ID)
x = make_unique<>("/watchdog/bond", "bond_123456")
x->start(); x->WaitUntilFormed();
b = make_unique<>("/watchdog/bond", "bond_123456")
b->start();
<===Bond established===>
node1.request("/watchdog/bond", "bond_987654")
"bond_987654" is not OK
return "bond_555555"
y = make_unique<>("/watchdog/bond", "bond_555555")
y->start(); y->WaitUntilFormed();
b = make_unique<>("/watchdog/bond", "bond_555555")
b->start();
<===Bond established===>


Thus, by adding suitable parameters to the Watchdog node and an extra parent class to existing nodes, I can monitor two arbitrary node and if one crashes I can inform the other.

So my questions are first, does what I am trying to do exist? And second, if it doesn't, does it make sense?

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