Add connection check at startup when out_forward.

[bootjp]

Added an option to check the out_forward node and communication when starting fluentd.

It is a matter with the following mailing list.
https://groups.google.com/forum/#!topic/fluentd/2ITnHbveYIM

Hello

I am using fluentd v1.2.6 in TLS encryption mode when forwarding in out_forward -> in_forward.

At fluentd startup I'd like to check if the out_forward process can connection with the in_forward node before listening for the forward port.
Does anyone know a good way about this?

The use case is below.
Existing applications are built across AWS and GCP, and the analysis base is in GCP.
I use out_forward TCP encryption for AWS and GCP connections.

The out_forward on the AWS side is redundant with the Active / Standby configuration.
When fluentd is deployed Switch from Active to Standby and return to the original Active / Standby when deployment is completed.

I think that it is desirable that fluentd gets an error as it is when the out_forward -> in_forward connection can not be performed by the new deployment so that the crash occurs.

The assumed error is a certificate validation failure or SHARD key mismatch.

• I recognize that these errors are not checked at startup in fluentd now

See you.

I am not familiar with Ruby, and since I read the Fluentd code for the first time this time, please let me know if there is a better implementation.

[repeatedly]

Thanks. Will check after flight.