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Add retries to getServer() (#316)

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Some backstory
==============

I was attempting to use postgres_exporter with the official Docker
container (https://hub.docker.com/_/postgres) In a Kubernetes
StatefulSet, with a side-car configuration, but found that I wasn't able
to connect even with sharing the Postgres Unix listening socket, between
both containers. After copying the container over to an Alpine base I
quickly found out that the postgres_exporter was actually starting
before the main Postres container had dropped the unix socket onto the
file system, a quick work around is to write a bash for loop checking
for the existence of a unix socket, however this would require
maintaining a container, besides other users may find retries useful on
startup.

Implementation
==============

All changes are made to the getServer function and variables are
local, I was unsure if it was worth adding command line switches but
this would allow for a more sophisticated backOff loop in the future.

Hope this help, and let me know if you would like me to changes
anything.
This commit is contained in:
Dan Molik 2019-10-29 23:54:18 -04:00 committed by Will Rouesnel
parent 238f5c099a
commit 043e68e067
1 changed files with 21 additions and 9 deletions
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30
cmd/postgres_exporter/postgres_exporter.go
View File

@ -863,17 +863,29 @@ func (s *Servers) GetServer(dsn string) (*Server, error) {
s.m.Lock()
defer s.m.Unlock()
var err error
server, ok := s.servers[dsn]
if !ok {
server, err = NewServer(dsn, s.opts...)
if err != nil {
var ok bool
errCount := 0 // start at zero because we increment before doing work
retries := 3
var server *Server
for {
if errCount++; errCount > retries {
return nil, err
}
s.servers[dsn] = server
}
if err = server.Ping(); err != nil {
delete(s.servers, dsn)
return nil, err
server, ok = s.servers[dsn]
if !ok {
server, err = NewServer(dsn, s.opts...)
if err != nil {
time.Sleep(time.Duration(errCount) * time.Second)
continue
}
s.servers[dsn] = server
}
if err = server.Ping(); err != nil {
delete(s.servers, dsn)
time.Sleep(time.Duration(errCount) * time.Second)
continue
}
break
}
return server, nil
}