On Thu, 4 Jun 2015, Brian Knox wrote:
I've been pondering other discovery support. So far, I've been wary of
introducing additional dependencies. There's so many discovery services
that are en vogue right now (zookeeper, etcd, consul...) and every
additional protocol supported is more overhead from a support and
maintenance standpoint.
This is exactly the problem.
If we start implementing specific discovery protocols, they will have to be
maintained for a long time, even when the fad fades and it's not a popular thing
any longer.
As far as I know, all of these support using name resolution for discovery
(either DNS or tweaking /etc/hosts) as well as their various proprietary
protocols, so as long as rsyslog does a name resolution check every time it
attempts to establish a new connection, these discovery tools could be used. DNS
propogation across the Internet is slow, but when used within your own network
you can disable all caching or set the cache to something very short. Normal
round-robin DNS (listing multiple IPs for one name) should result in queries
returning different answers even when caching is involved.
So, Rsyslog will connect to whatever the service discovery system says is
correct, and it can be configured to reconnect every X messages (and it will
reconnect if it gets disconnected due to any error)
This should mean nothing is needed on the initiating (client) side.
On the receiving (server) side, there shouldn't be anything that needs to happen
either. The service discovery system needs to setup a health check of some kind
to decide if rsyslog is healthy or not, and if it is, it is part of the cluster,
if not, it's cut out. This is no different than using any other load balancer
(it can be "does it accept a TCP connection", or "does it accept a message", or
"does it recieve a message and output it to a specific destination" depending on
how paranoid you are)
unless rsyslog is caching name lookups for outbound connections, there should be
nothing that needs to be changed in rsyslog.
David Lang
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