Saving a value to ngx.var in init_by_lua*, to be used in an upstream{} block

ulidtko · 2019-01-22T21:01:08+00:00

Hi all- I have been a member for awhile and now working in SV... when is the next meeting? I can finally attend in person :)

Saving a value to ngx.var in init_by_lua*, to be used in an upstream{} block

ulidtko

Hi everyone!

I'm dealing with a not-so-small configuration system written in a mixture of Lua and the usual Nginx syntax. There're limits on what I can realistically change/rewrite in this system.

To spare you with unimportant details, here's (a part of) /etc/nginx/upstream-defs.conf:

upstream local_foobar {
set_by_lua $foobar_port "FOOBAR_PORT";
server http://localhost:$foobar_port;
}

That segment is include-d from the top-level nginx.conf like this:

http {
init_by_lua_block {

FOOBAR_PORT = os.getenv('FOOBAR_SERVER_PORT') or "12345"
-- ngx.var.foobar_port = FOOBAR_PORT

}

include /etc/nginx/upstream-defs.conf;
}

Here's where I need help: I have to keep the computation of FOOBAR_PORT (Lua global, yes, sorry) as it is, and somehow use its value in an upstream block.

The way it's written above -- set_by_lua $foobar_port "FOOBAR_PORT" -- doesn't work:

2019/01/22 14:27:06 [emerg] 2767#0: "set_by_lua" directive is not allowed here in /etc/nginx/nginx.conf:138

-- which I can understand, since this use of set_by_lua is neither in a valid context, neither during appropriate phase (access/rewrite VS init).

But it's unclear to me what else I can try. Naïve assignment to ngx.var.foobar_port (commented above) doesn't work, too:

2019/01/22 14:33:13 [emerg] 3390#0: invalid host in upstream "http://localhost:$foobar_port" in /etc/nginx/nginx.conf:141

Any suggestions?.. Thanks in advance.

ulidtko

I think I figured it out:

upstream local_foobar {

server 0.0.0.1; # intentionally invalid placeholder

balancer_by_lua_block {

local balancer = require 'ngx.balancer'

local ok, err = balancer.set_current_peer('127.0.0.1', FOOBAR_PORT)

if not ok then return ngx.exit(ngx.HTTP_INTERNAL_SERVER_ERROR) end

}

Thanks for listening! :)

On Tuesday, January 22, 2019 at 3:01:08 PM UTC+2, Max ulidtko wrote:

Hi everyone!

I'm dealing with a not-so-small configuration system written in a mixture of Lua and the usual Nginx syntax. There're limits on what I can realistically change/rewrite in this system.

To spare you with unimportant details, here's (a part of) /etc/nginx/upstream-defs.conf:

upstream local_foobar {
set_by_lua $foobar_port "FOOBAR_PORT";
server http://localhost:$foobar_port;
}

That segment is include-d from the top-level nginx.conf like this:

http {
init_by_lua_block {

FOOBAR_PORT = os.getenv('FOOBAR_SERVER_PORT') or "12345"
-- ngx.var.foobar_port = FOOBAR_PORT
}
include /etc/nginx/upstream-defs.conf;
}

Here's where I need help: I have to keep the computation of FOOBAR_PORT (Lua global, yes, sorry) as it is, and somehow use its value in an upstream block.

The way it's written above -- set_by_lua $foobar_port "FOOBAR_PORT" -- doesn't work:

2019/01/22 14:27:06 [emerg] 2767#0: "set_by_lua" directive is not allowed here in /etc/nginx/nginx.conf:138

-- which I can understand, since this use of set_by_lua is neither in a valid context, neither during appropriate phase (access/rewrite VS init).

But it's unclear to me what else I can try. Naïve assignment to ngx.var.foobar_port (commented above) doesn't work, too:

2019/01/22 14:33:13 [emerg] 3390#0: invalid host in upstream "http://localhost:$foobar_port" in /etc/nginx/nginx.conf:141

Any suggestions?.. Thanks in advance.