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#Gatekeeper: NGINX co-process for SOA-style infrastructures

Gatekeeper turns NGINX into your edge service. Gatekeeper watches your Zookeeper service discovery paths and dynamically builds NGINX upstreams for them. Load balancers (ELBs especially) can be SPOFs and are the first steps to madness. Cut out the middle man and let NGINX manage your upstream load balancing.

Gatekeeper uses Mustache templates to build upstreams and locations using your existing nginx.conf.

events {
    worker_connections  4096;
}

http {
    {{#clusters}}
        upstream {{clusterName}} {
        {{#servers}}
            server {{host}}:{{port}};
        {{/servers}}
            keepalive 24;
        }
    {{/clusters}}
    server {
        port 80;

        {{#locations}}
            location {{context}} {
            {{#upstream}}
                proxy_pass              {{protocol}}://{{clusterName}};
            {{/upstream}}
            {{#attributes}}
                {{key}}                 {{value}}
            {{/attributes}}
            }
        {{/locations}}
    }
}

With two small blocks of customizable templating, each time a node is registered or deregistered a new nginx.conf is written and NGINX sent a SIGHUP.

You'll need a NGINX config template and a gatekeeper.properties. There are defaults included in nginx.conf.mustache.default and gatekeeper.properties.default.

Important: Configuration changes are automatically reloaded. This may change in the future to require a SIGHUP.

Any additional configuration (e.g. FQDN, SSL, listeners, etc.) can be done in nginx.conf as you'd normally do. You can even include a default upstream and default context directly in the template.

Your gatekeeper.properties and nginx.conf.mustache should be managed by a configuration management platform, e.g. Chef/Ansible/Puppet.

In your gatekeeper.properties you'll need to define clusters, which will become your NGINX upstreams. These clusters correspond to cluster names you've defined using your service discovery extension.

The namespace is by default null, e.g. the root path. I use /discovery, which ensures that Curator can't accidentally have any namespace collisions with other services.

Discovery Path is the znode under which all of your services then make a znode for themselves.

/discovery (namespace)
        /services (discoveryPath)
                /service-a (cluster)
                      instance-1
                      instance-2
                /service-b
                      instance-1
                      instance-2
                      instance-3

Config for the above looks like this:

zookeeper.quorum=zookeeper1.mycompany.com
zookeeper.namespace=discovery
zookeeper.discoveryPath=/services

# Upstreams to look for
clusters=service-a,service-b

Each cluster can then be assigned various contexts for routing. Future work will push this config into ZooKeeper.

# Proxy_pass locations, comma-separated lists
cluster.service-a.context=/a
cluster.service-b.context=/,/b

Build the agent as you would normally

mvn package

A jar will be built in gatekeeper-agent/target/gatekeeper-agent-1.0.1.jar. Take this jar and put it on your NGINX servers.

You can run the agent as below:

java -jar gatekeeper.jar -c /path/to/gatekeeper.properties

or for the default `gatekeeper.properties`

java -jar gatekeeper.jar

I prefer to run Gatekeeper under Supervisord. A config for Gatekeeper looks like this:

[program:gatekeeper]
directory=/opt/gatekeeper
command=java -Xmx128m -Xss256k -jar gatekeeper-agent.jar -c gatekeeper.properties
redirect_stderr=true
stdout_logfile=/var/log/gatekeeper.log

It's also quite helpful to have centralized configuration management. Changes to the NGINX template can be made via Chef cookbook, or Ansible Playbook. Gatekeeper does not come with any configuration management utilities.

Send a SIGHUP to the Gatekeeper process.

kill -HUP <pid of gatekeeper process>

You should see a message in the log.

You'll generally want to compile this yourself, but core is available on Clojars for extension building:

<dependency>
    <groupId>com.xorlev.gatekeeper</groupId>
    <artifactId>gatekeeper-core</artifactId>
    <version>1.0.1</version>
</dependency>

Currently only supports Netflix Curator Service Discovery Extensions. Other implementations are trivial and can be implemented by including gatekeeper-core, and including your dependency in the resulting gatekeeper-agent build.

You can build gatekeeper with a different module like so:

mvn package -discovery.package=gatekeeper-some-discovery-module

I'm not good at C, I believe I'd make a leaky C-module. I am confident in my ability to write a stable Java co-process. Additionally, Netflix's Curator library is also top-notch, better than any stock Zookeeper library around.

##License Copyright 2014 Michael Rose

Licensed under the Apache License, Version 2.0 (the "License"); you may not use this work except in compliance with the License. You may obtain a copy of the License in the LICENSE file, or at:

http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License.