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consul: Library to interface with the consul HTTP API from nginx-module-lua

Installation

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CentOS/RHEL 6, 7, 8 or Amazon Linux 2

yum -y install https://extras.getpagespeed.com/release-latest.rpm
yum -y install lua-resty-consul

To use this Lua library with NGINX, ensure that nginx-module-lua is installed.

This document describes lua-resty-consul v0.4.0 released on Aug 18 2021.


Library to interface with the consul HTTP API from ngx_lua

Overview

Methods all return a lua-resty-http response object.
The response body has been read and set to res.body, JSON decoded if the response has a Content-Type header of Application/JSON.

All response headers are available at res.headers.

The ACL Token parameter is always sent as the X-Consul-Token header rather than being included in the query string.

If wait or index arguments are provided the request read timeout is extended appropriately.
wait must be passed as a number of seconds, do not include s or any other unit string.

local resty_consul = require('resty.consul')
local consul = resty_consul:new({
        host            = "127.0.0.1",
        port            = 8500,
        connect_timeout = (60*1000), -- 60s
        read_timeout    = (60*1000), -- 60s
        default_args    = {
            token = "my-default-token"
        },
        ssl             = false,
        ssl_verify      = true,
        sni_host        = nil,
    })

local res, err = consul:get('/agent/services')
if not res then
    ngx.log(ngx.ERR, err)
    return
end

ngx.print(res.status) -- 200
local services = res.body -- JSON decoded response


local res, err = consul:put('/agent/service/register', my_service_definition, { token = "override-token" })
if not res then
    ngx.log(ngx.ERR, err)
    return
end

ngx.print(res.status) -- 200
ngx.print(res.headers["X-Consul-Knownleader"]) -- "true"
local service_register_response = res.body -- JSON decoded response


local res, err = consul:list_keys() -- Get all keys
if not res then
    ngx.log(ngx.ERR, err)
    return
end

local keys = {}
if res.status == 200 then
    keys = res.body
end

for _, key in ipairs(keys) do
    local res, err = consul:get_key(key)
    if not res then
        ngx.log(ngx.ERR, err)
        return
    end

    ngx.print(res.body[1].Value) -- Key value after base64 decoding
end

Basic Methods

new

syntax: client = consul:new(opts?)

Create a new consul client. opts is a table setting the following options:

  • host Defaults to 127.0.0.1
  • port Defaults to 8500. Set to 0 if using a unix socket as host.
  • connect_timeout Connection timeout in ms. Defaults to 60s
  • read_timeout Read timeout in ms. Defaults to 60s
  • default_args Table of query string arguments to send with all requests (e.g. token) Defaults to empty
  • ssl Boolean, enable HTTPS requests. Default to false.
  • ssl_verify Boolean, verify SSL certificates. Defaults to true = true,
  • sni_host Hostname to use when verifying SSL certs.

get

syntax: res, err = consul:get(path, args?)

Performs a GET request to the provided path. API Version is automatically prepended.

args is a table of query string parameters to add to the URI.

Returns a lua-resty-http response object.
On error returns nil and an error message.

put

syntax: res, err = consul:put(path, body, args?)

Performs a PUT request to the provided path. API Version is automatically prepended.

args is table of query string parameters to add to the URI.

If body is a table or boolean value it is automatically json encoded before being sent.
Otherwise anything that lua-resty-http accepts as a body input is valid.

Returns a lua-resty-http response object.
On error returns nil and an error message.

delete

syntax: res, err = consul:delete(path, args?)

Performs a GET request to the provided path. API Version is automatically prepended.

args is a table of query string parameters to add to the URI.

Returns a lua-resty-http response object.
On error returns nil and an error message.

get_client_body_reader

Proxy method to lua-resty-http

Key Value Helpers

These methods automatically prepend /v1/kv, only the actual key should be passed.
Base64 encoded values are automatically decoded.

get_key

syntax: res, err = consul:get_key(key, args?)

Retrieve a Consul KV key. Values are Base64 decoded.

args is a table of query string parameters to add to the URI.

Returns a lua-resty-http response object.
On error returns nil and an error message.

put_key

syntax: res, err = consul:put_key(key, value, args?)

Create or update a KV key.

args is table of query string parameters to add to the URI.

If value is a table or boolean value it is automatically json encoded before being sent.
Otherwise anything that lua-resty-http accepts as a body input is valid.

Returns a lua-resty-http response object.
On error returns nil and an error message.

delete

syntax: res, err = consul:delete_key(key, args?)

Delete a KV entry.

args is a table of query string parameters to add to the URI.

Returns a lua-resty-http response object.
On error returns nil and an error message.

list_keys

syntax: res, err = consul:list_keys(prefix?, args?)

Retrieve all the keys in the KV strore. Optionally within a prefix.

args is a table of query string parameters to add to the URI.
keys is always set as a query string parameter with this method

Returns a lua-resty-http response object.
On error returns nil and an error message.

Transaction Helper

txn

syntax: res, err = consul:txn(payload, args?)

Performs a PUT request to the /v1/txn API endpoint with the provided payload.

payload can be provided as a Lua table, in which case Value keys will be automatically base64 encoded.
Otherwise anything that lua-resty-http accepts as a body input is valid.

Returns a lua-resty-http response object.
On error returns nil and an error message.

KV values in the response body are automatically base64 decoded.

local txn_payload = {
    {
        KV = {
            Verb   = "set",
            Key    = "foo",
            Value  = "bar",
        }
    },
    {
        KV = {
            Verb   = "get",
            Key    = "foobar",
        }
    }
}

local consul = resty_consul:new()

local res, err = consul:txn(txn_payload)
if not res then
    ngx.say(err)
    return
end

ngx.say(res.body.Results[2].KV.Value) -- "bar"

GitHub

You may find additional configuration tips and documentation for this module in the GitHub repository for nginx-module-consul.

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