Writing to NGINX config space

[Blaine Morgan]

Is there a way to write/rewrite the config file in lua?  I have a small DSL but the effects are spread across rewrite_by_lua_block, body_filter_by_lua_block, and a log_by_lua_block.  I was thinking to have the DSL generate config output.

[Robert Paprocki]

"In Lua"? Sure, but outside the context of openresty- at least, the worker processes. What you're describing is essentially config management. Chef/puppet/ansible/salt/waffle/whatever seems like the right choice here?

On Jun 18, 2018, at 15:56, Blaine Morgan <nbmo...@gmail.com> wrote:

Is there a way to write/rewrite the config file in lua?  I have a small DSL but the effects are spread across rewrite_by_lua_block, body_filter_by_lua_block, and a log_by_lua_block.  I was thinking to have the DSL generate config output.

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[Blaine Morgan]

I was thinking in the init by lua phase.

The languages for templates are not as conducive for building a simple DSL so I wanted to use the init_by_lua phase. But in my passes in the nginx lua ref I didn't see how to write config

[Thibault Charbonnier]

On 06/18/2018 09:14 PM, Blaine Morgan wrote:
> I was thinking in the init by lua phase.
>
> The languages for templates are not as conducive for building a simple
> DSL so I wanted to use the init_by_lua phase. But in my passes in the
> nginx lua ref I didn't see how to write config

Could you elaborate on what you are trying to accomplish, specifically?
It is unclear. And what do you mean by "the effects are spread across ..."?

The init_by_lua phase runs _during_ the Nginx configuration parsing (or
even after if you have a lua_shared_dict defined), so you have to
manipulate the internal structures maintained by Nginx.

A few months ago, I tried to promote a new way to configure
ngx_lua-specific settings via a new configure_by_lua phase:

https://github.com/openresty/lua-nginx-module/pull/1259

The ultimate goal was to be able to configure server or location blocks
right from within Lua, but as you can see from the thread, it was not
accepted. As of today, you are likely better off with templating your
configuration as suggested by Robert.

Best,
Thibault

[Blaine Morgan]

Sure I am working on a router that is specific to my business. Its job is to make legacy systems "behave" as newer ones.  Some protocols will have enough info in headers. These make us happy 😊.  There are older arcane legacy protocols that just behave badly. There is no way to upgrade them as the data is being sent by devices in the field. These require some body inspection. Fortunately there body sizes are very small and well ordered/defined.

I want a dsl that finds the_id and looks like:

Url: /ABC/xyz/, use: header inspection a, with params

Url: /DEF/uvw/, use: body dig, params

Url: /GHI/rest/, use: man in the middle, params

...

I need about 40 such lines. 

The man in the middle records a new identifier that is later a synonym for the id

You would never design something like this on purpose from scratch, but to "de-snoflake" legacy...  The result of this bailing wire is a correct id header so the rest of the system can treat the traffic with normal tools and to encapsulate the legacy packet conversion handling to one place.

These rules cross multiple lua block types form header, body, response, and logging.  It seems that it would be DRYer to emit the config from a simple DSL parser.  Maybe an include by lua block?

Why do I need funky routing, we're moving to AWS and things that worked in a hand-tossed world could be made way more adaptive and resilient post the lift and shift efforts. But the code on the devices and in the containers is *not* going to change. But, I want to move and balance container loads.  Oh, for various reasons we also lose the origin ip. 

[Robert Paprocki]

If you have an DSL and you need to parse it to write an Nginx config file, that still sounds like the job of a config management tool, not something the master Nginx process should to do rewrite its own config (which sounds like a nightmare, IMO).

It makes sense to have OpenResty do routing/parsing logic when runtime changes need to occur, or Nginx's trie location block can't handle your business logic. But it sounds like you're trying to write out an Nginx config file, so that seems like not an appropriate usage here? My $0.02.

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