lua-local-resolver

Resolve hostname which is written in local hosts definition file (e.g. /etc/hosts).

Motivation

This library will be useful for using openresty, this solves some issue about resolving hosts related problems.

resty.redis couldn't resolve localhost to 127.0.0.1 -- issue
The host argument on ngx.balancer.set_current_peer() couldn't accept hostname, only ip address -- issue
When we use docker with linking other containers, we want to resolve linked host via /etc/hosts

To solve above things, parse host definition file and resolve hostname to local ip address.

Usage

-- Add package and require library
package.path = package.path .. ";/path/to/project/lua-local-resolver/?.lua"

local resolver = require "local-resolver"

-- Instantiate with host definition file path
local r = resolver.new("/etc/hosts")

-- Resolve hostname
print(r:resolve("localhost")) -- 127.0.0.1

With Openresty

Intialize at init_by_lua directive:

init_by_lua_block {
  local resolver = require "local-resolver"

  -- expose global as we expect
  resolver = resolver.new("/etc/hosts")
}

and use it following directives.

Balancer example:

balancer_by_lua_block {
  local balancer = require "ngx.balancer"
  -- resolve localhost to ip
  local ok, err = balancer.set_current_peer(resolver:resolve("localhost"), 80)
  ...

  -- Or, use linked docker container name
  local ok, err = balancer.set_current_peer(resolver:resolve("docker-linked-name"), 80)
  ...
}

Redis example:

content_by_lua_block {
  local redis = require "resty.redis"
  local r = redis:new()

  -- connect with hostname
  local ok, err = r:connect(resolver:resolve("localhost"), 6379)
  ...
}

No longer you don't need to define environment variable like REDIS_HOST at nginx.conf :)

Note

Of course this library only resolves local definition hosts. So, if you want to resolve external hosts, we prefer to use lua-resty-dns, it is bundled in openresty.

Author

Yoshiaki Sugimoto

License

MIT