Option to cloud-init template and TF to modify ulimit for file process

[rickardl]

Adds option to TF module to change soft and hard limit, fixes #10

[neilh456]

Why can we not put this in the AMI. We could increase the limits in
/etc/security/limits.conf

•     hard    nofile      100000
  

•     soft    nofile      100000
  

hard nofile 100000
soft nofile 100000

Or system wide in /etc/sysctl.conf
fs.file-max = 100000

Just a question, I can approve afterwards

[itsdalmo]

Looking at e.g. the below issue, it seems like the limit needs to be set outside the systemd.unit:
syncthing/syncthing#5319 (comment)

Are you sure this works/have you tested it?

edit:

Here is an example configuration from a concourse issue:
concourse/concourse#480 (comment)

[Unit]
Description=Concourse Worker
After=network.target

[Service]
EnvironmentFile=/opt/concourse/etc/worker.conf
ExecStart=/opt/concourse/bin/concourse worker
KillMode=process
LimitNPROC=infinity
LimitNOFILE=infinity
TasksMax=infinity
Restart=on-failure
RestartSec=3
ExecStop=/bin/kill -USR2 $MAINPID ; /usr/bin/tail --pid $MAINPID -f /dev/null
TimeoutStopSec=300

[Install]
WantedBy=multi-user.target