testing: retry MgoDial

testing: retry MgoDial

Because mongod is not ready to accept connections immediately on start
we can attempt do Dial mongo before it is ready to accept connections.

Introduce a short retry attempt to give us a better chance at getting a 
successful connection.

https://code.launchpad.net/~dave-cheney/juju-core/034-testing-mongo-not-ready/+merge/132150

(do not edit description out of merge proposal)

[dave_cheney.net, 2012-10-30 15:55:46]

Please take a look.

[fwereade, 2012-10-31 10:40:13]

LGTM

[niemeyer, 2012-11-01 14:32:38]

https://codereview.appspot.com/6822056/diff/1/testing/mgo.go
File testing/mgo.go (right):

https://codereview.appspot.com/6822056/diff/1/testing/mgo.go#newcode102
testing/mgo.go:102: for a := mgoDialAttempt.Start(); a.Next(); {
Have you seen mgo.DialWithTimeout? Does it not solve the problem?

[dave_cheney.net, 2012-11-01 14:33:31]

The worrying thing is, mgo.Dial already calls mgo.DialWithTimeout(10s).

i'm not sure if this small attempt will really fix the problem.

On Fri, Nov 2, 2012 at 1:32 AM,  <n13m3y3r@gmail.com> wrote:
>
> https://codereview.appspot.com/6822056/diff/1/testing/mgo.go
> File testing/mgo.go (right):
>
> https://codereview.appspot.com/6822056/diff/1/testing/mgo.go#newcode102
> testing/mgo.go:102: for a := mgoDialAttempt.Start(); a.Next(); {
> Have you seen mgo.DialWithTimeout? Does it not solve the problem?
>
> https://codereview.appspot.com/6822056/

[niemeyer, 2012-11-01 14:48:53]

On 2012/11/01 14:33:31, dfc wrote:
> The worrying thing is, mgo.Dial already calls mgo.DialWithTimeout(10s).
> 
> i'm not sure if this small attempt will really fix the problem.

Exactly. I don't really understand why 10s + 500ms will work when 10s doesn't.