[Feature request] Add lock option to the IPtables input plugin

[ldep30]

Feature Request

Proposal:

Add an option allowing to pass the -w argument to the Iptables command called by the plugin

Current behavior:

Iptables commands are launched without any lock argument

Desired behavior:

Add an option like use_lock = true|false to the plugin configuration. If the option is set to true, then add -w to the Iptables arguments.

Use case:

In our case, using multiple inputs.iptables plugins can lead to concurrent Iptables access resulting in "ERROR in input [inputs.iptables]: exit status 4" messages in telegraf.log and missing metrics. This can be partially fixed using collection_jitter = "3s" in the agent section of telegraf.conf, but this is not an ideal solution. The -w switch should solve the problem according to the Iptables man page :

-w, --wait
Wait for the xtables lock. To prevent multiple instances of the program from running concurrently, an attempt will be made to obtain an exclusive lock at launch. By default, the program will exit if the lock cannot be obtained. This option will make the program wait until the exclusive lock can be obtained.

[sspaink]

Resolved by #2201