AWSnycast is a routing daemon for AWS route tables, to simulate an Anycast like service, and act as an extension of in-datacenter Anycast. It can also be used to provide HA NAT service.

A common pattern in AWS is to route egressing traffic (from private subnets) through a NAT instance in a public subnet. AWSnycast can manage one or more NAT instances for you automatically, allowing you to deploy one or more NAT instances per VPC.

You can deploy 2 NAT machines, in different availability zones, and configure a private routing table for each AZ. AWSnycast can then be used to manage the routes to these NAT machines for High Availability, such that by default, both machines will be active (for their AZ - to avoid cross AZ transfer costs + latency), however if one machine fails, then the remaining machine will take over it's route for the duration that it's down.

In datacenters, a common pattern is to have a /24 network for Anycast, and then in each datacenter, use systems like exabgp and bird on hosts to publish BGP routing information for individual /32 IPs of services they're running.

In AWS we can configure VPN tunnels, or Direct Connects, and publish routes to the Amazon routing tables using BGP, including the Anycast /24. AWSnycast then runs locally on your AWS nodes, healthchecks local services, and publishes more specific routes to them into the AWS route table.

This means that all your systems in AWS can use the same network for Anycast services as your in datacenter machines, and talk to services locally, as you bring them up in AWS. This is super useful for bootstrapping a new VPC (before you have any local services running), or for providing high availability.

You don't have to have a datacenter or VPN connection for AWSnycast to be useful to you, you still get route publishing based on healthchecks, and HA/failover, just not bootstrapping from in-datacenter.

N.B. Whilst publishing routes from AWS into your datacenter's BGP would be useful, at this time that is beyond the goals for this project.

You can setup routes in AWS to go to an individual instance. This means that you inject routes that are outside the addesses space for your VPC, and point them to an instance, failing over to a different instance if the machine providing the service fails.

All you have to do on the instance itself is setup a network interface which can deal with this traffic; for example, alias lo0:0 as 192.168.1.1 and disable source/destination checking for that instance in AWS.

By advertising a larger range via BGP (from VPN or Direct connect) and then injecting /32 routes for the AWS instances of individual services, you get both bootstrapping (being able to bootstrap new AWS regions from a VPN connection, as critical services such as dns and puppet/chef are always at a fixed IP address) and HA.

Good question! You can provide HA in AWS by assigning each service an ENI, and moving them between healthy instances.

There are a number of reasons I chose not to do this:

• Most AWS machine classes/sizes are fairly restricted about the number of ENIs they can have attached.
• ENIs need to be detached then re-attached - so failover isn't atomic and it makes writing reliable distributed software to do this hard without a strong consensus store. (Think detach-fight!)
• I explicitly didn't want to depend on a strong consensus store (to make this useful for VPC bootstrapping).
• ENIs are an AWS only solution, and don't/can't provide parity with existing Anycast implementations in datacenter.

Basic infrastructure services, like DNS (if you use your own DNS already), puppet or chef servers, package repositories, etc. This is not a load balancing, or SOA service discovery solution.

I'd highly recommend putting any TCP service you use AWSnycast for behind haproxy, for load balancing (as only one route can be active at a time), and to make AWSnycast's failover only needed when an instance dies, rather than an individual service instance.

If you're building an SOA, and for 'application level' rather than 'infrastructure level' services, I'd recommend checking out Consul, Smartstack and similar technologies.

In the tests/integration folder, there is Terraform code which will build a simple AWS VPC, with 2 AZs and 2 NAT machines (with HA and failover), and AWSnycast setup.

To try this, you can just run make then terraform apply in that directory to build the example network, then make sshnat to log into one of the machines, and journalctl -u awsnycast to view the logs.

Try terminating one of the machines and watch routes fail over!

Or try running:

sudo iptables -I OUTPUT -d 8.8.8.8 -j DROP

to kill the healthcheck on one machine, and watch it drop the route and the other machine pick it up.

You can install binary release versions onto x68 Linux directly from github, e.g.

sudo wget https://github.com/bobtfish/AWSnycast/releases/download/v0.0.1/AWSnycast -O /usr/local/bin/AWSnycast
sudo chmod 700 /usr/local/bin/AWSnycast

You need go installed to build this project (go 1.4 or 1.5).

Once you have go installed, and a GOPATH setup, you should be able to install with:

go get github.com/bobtfish/AWSnycast
go install github.com/bobtfish/AWSnycast

This will install the software to the bin directory in the first part of your GOPATH.

Run this to find it:

echo $(echo $GOPATH|cut -d: -f1)/bin/AWSnycast

You can run AWSnycast -h to get a list of helpful options:

Usage of AWSnycast:
  -debug
        Enable debugging
  -f string
        Configration file (default "/etc/awsnycast.yaml")
  -noop
        Don't actually *do* anything, just print what would be done
  -oneshot
        Run route table manipulation exactly once, ignoring healthchecks, then exit

Once you've got it fully setup, you shouldn't need any options.

To run it also needs permissions to access the AWS API. This can be done either by supplying the standard AWS_ACCESS_KEY_ID and AWS_SECRET_ACCESS_KEY environment variables, or by applying an IAM Role to the instance running AWSnycast (recommended).

An example IAM Policy is shown below:

{
  "Version": "2012-10-17",
  "Statement": [
        {
            "Action": [
                "ec2:ReplaceRoute",
                "ec2:CreateRoute",
                "ec2:DeleteRoute",
                "ec2:DescribeRouteTables"
            ],
            "Effect": "Allow",
            "Resource": "*"
        }
    ]
}

Note that this software does not need root permissions, and therefore should not be run as root on your system. Please run it as a normal user (or even as nobody if you're using an IAM Role).

Which routes to advertise into which route tables is configured with a YAML config file.

By default AWSnycast will look for this in /etc/awsnycast.yaml

An example config is shown below:

    ---
    poll_time: 300 # How often to poll AWS route tables
    healthchecks:
        public:
            type: ping
            destination: 8.8.8.8
            rise: 2  # How many need to succeed in a row to be up
            fall: 10 # How many need to fail in a row to be down
            every: 1 # How often, in seconds
        localservice:
            type: tcp
            destination: 192.168.1.1
            rise: 2
            fall: 2
            every: 30
            send: HEAD / HTTP/1.0 # String to send (optional)
            expect: 200 OK        # Response to get back (optional)
    remote_healthchecks: # N.B. This is a WIP - doesn't work yet!
        service:
            type: tcp
            rise: 2
            fall: 2
            every: 30
            send: HEAD / HTTP/1.0 # String to send (optional)
            expect: 200 OK        # Response to get back (optional)
    routetables:
        # This is our AZ, so always try to takeover routes always
        a:
            find:
                type: by_tag
                config:
                    key: Name
                    value: private a
            manage_routes:
              - cidr: 0.0.0.0/0     # NAT box, so manage the default route
                instance: SELF
                healthcheck: public
              - cidr: 192.168.1.1/32 # Manage an AWSnycast service on this machine
                instance: SELF
                healthcheck: localservice
                remote_healthcheck: service # WIP - ignored currently!
        # This is not our AZ, so only takeover routes only if they don't exist already, or
        # the instance serving them is dead (terminated or stopped).
        # Every backup AWSnycast instance should have if_unhealthy: true set for route tables
        # it is the backup server for, otherwise multiple instances can cause routes to flap
        b:
            find:
                type: by_tag
                config:
                    key: Name
                    value: private b
            manage_routes:
              - cidr: 0.0.0.0/0
                if_unhealthy: true # Note this is what causes routes only to be taken over not present currently, or the instance with them has failed
                instance: SELF
                healthcheck: public
              - cidr: 192.168.1.1/32
                if_unhealthy: true
                instance: SELF
                healthcheck: localservice

Release (stable) versions of AWSnycast are tagged in the repository, and go binaries (generated by Travis CI) are uploaded to github - see the CHANGELOG.md for information about what is in each release.

Note that currently this project is pre-1.0, so I reserve the right to make massive sweeping changes between versions.

Also, I've properly tested only the stuff in tests/integration, so YMMV and this may eat your lunch, and completely mess up your AWS account! You are HIGHLY recommended to become confident using the -noop mode before running this for real!

Once I've got something that I am happy deploying to production, I'll cut a 1.0.0 and switch to semver.

This project is currently under heavy development.

Bugs to fix:

• Fix not deleting routes when healthcheck goes unhealthy sometimes
• Fix issue when we try to change a route, and it's been deleted under us (re-add it)

Here's a list of the features that I'm planning to work on next, in approximate order:

• Make us autodetect the VPC this instance is running in, and refuse to adjust routing tables in other VPCs
• Make route table finding more flexible - be able to search by more than tag, and be able to interpolate current AZ
• Make how often we poll AWS for route tables configurable
• Enable the use of multiple different healthchecks for a route (to only consider it down if multiple checks fail)
• Make how often we poll AWS for route tables flexible (max/min times, and backoff)
• Implement 'negative' healthchecks, to be able to check the routes currently managed by other instances, and takeover faster than the other instance deleting it's route + polling time.
• Add serf gossip between instances, to allow faster and reliable failover/STONITH
• Add the ability to have external clients participate in healthchecks in the serf network.
• Add a web interface to be able to get the state (and manually initiate failovers?)

Bug reports, success(or failure) stories, questions, suggestions, feature requests and (documentation or code) patches are all very welcome.

Please feel free to ping t0m on Freenode or @bobtfish on Twitter if you'd like help configuring/using/debugging/improving this software.

Please note however that this project is released with a Contributor Code of Conduct. By participating in this project you agree to abide by its terms.

Copyright Tomas Doran 2015

Apache2 - See the included LICENSE file for more details.