set a maximum limit for the forks per job

[anxstj]

ISSUE TYPE

• Feature Idea

SUMMARY

In small environments (one node setups) a job may increase the maximum capacity in terms of forks which might crash the system.
Therefore I suggest a global options (maybe per instance) which sets a limit for the number of forks per job. If a job increases this limit it should be prevented from running or saving the job template should result in an error.

[wenottingham]

This is actualy needed in larger setups more often.

[ryanpetrello]

@matburt @jakemcdermott @wenottingham

https://github.com/ansible/awx/pull/5604/files#diff-82158f398fa5f587f3a95c3060cb05c9R622

Should we set some sane default for all new installs so people don't have to type in 1000 and induce a nuclear meltdown to learn this setting exists? I recall the core folks basically saying there was a theoretical limit anyways where Ansible couldn't keep up, and that raising it would only make things worse.

[matburt]

The solution looks good to me.

[elyezer]

Did this in order to verify this one:

1. Updated the MAX_FORKS to 4 on the Jobs settings
2. Tried to set a job template max forks option to anything greater than 4. It provided the expected validation error.
3. Left the job template max forks set to 4 and updated the MAX_FORKS to 1 on the settings page.
4. Triggered the job template and, as expected, the following log message was printed:

awx_1        | 2020-02-11 19:17:21,461 WARNING  awx.main.tasks Maximum number of forks (1) exceeded.

With all that we can consider this issue verified.