maglev0

Faux-maglev-style hashing for managing VIPs using Iptables CLUSTERIP and Zookeeper. Not sanctioned or supported by Google in any way.

Description

maglev0 is a proof-of-concept tool to implement "maglev"-style consistent hashing with Linux's CLUSTERIP iptables rules.

CLUSTERIP allows for N servers to share the burden of respondig to requests on an IP (vip), contrast to the traditional HA Active/Standby failover techniques where N=2. ("seesaw"-style)

The hard part is managing which nodes respond to which requests. With Active/Standby techniques you can use off-the-shelf clustering software (keepalived, seesaw, heartbeat, etc). When N>2, something has to divide up the work fairly and handle re-balancing when nodes change. This is what maglev0 does.

maglev0 uses zookeeper for sharing a consistent view of the world with peers. For balancing and reacting to node changes, it uses Google's maglev hashing algorithm to minimize disruption.

Limitations

maglev0 doesn't actually load balance anything, really. It is more like a "router-less router", where each node opts in to responding for packets it thinks it is responsible for, ignoring the rest. It is more akin to ECMP without the router help. This is the reasoning behind the 0 in maglev0: It implements the first "layer" of routing that maglev-powered loadbalancers need, the ECMP-style routing.

Future work might include using something other than CLUSTERIP, which is an old (underrated?) technology that does not work in "cloud" environments. Additionally, the design of CLUSTERIP requires that all inbound traffic reach all nodes. For some workloads this is unacceptable.

Also I'm pretty sure I'm not using the algorithm correctly, it doesn't "seem" very balanced (could be due to the small ring size)

Setup

If your gopath is ready, you can use go install:

go install github.com/solarkennedy/maglev0

Before maglev0 can manipulate iptables for CLUSTERIP, the rule must be added. This usually would happen with a startup script:

iptables --insert INPUT --destination 198.51.100.1 \
  --jump CLUSTERIP --new --hashmode sourceip --clustermac 01:aa:7b:47:f7:d7 \
  --total-nodes 5 --local-node 1 --interface eth0

Then you can run maglev0 to manage which nodes that CLUSTERIP responds to:

maglev0 --my-id=1 --total-nodes=5 --cluster-ip=198.51.100.1

Usage

Usage:
  maglev0 [--my-id=ID] [--total-nodes=N] [--zk=ZK] [--cluster-ip=IP]

Options:
  --my-id=<ID>      Specify the local node id, starting from 1. Must be unique throughout the cluster. [default: 1]
  --total-nodes=<N> Total nodes in the cluster. Can be more than the number of physical nodes available. [default: 5]
  --zk=<ZK>         Zookeeper connection string in csv format. [default: localhost:2181]
  --cluster-ip=<IP> Cluster ip (vip) to manage. [default: 198.51.100.1]
  -h, --help        Show this screen

Example Output

sudo ./maglev0
map[--my-id:1 --total-nodes:<nil> --zk:localhost:2181 --cluster-ip:<nil>]
2016/11/20 17:54:02 Connected to [::1]:2181
2016/11/20 17:54:02 Authenticated: id=96972190335828052, timeout=4000
2016/11/20 17:54:02 Re-submitting `0` credentials after reconnect
...

[1 3 4]
backend-4 is responsible for node 1
backend-3 is responsible for node 2
backend-1 (me!) is responsible for node 3
backend-4 is responsible for node 4
backend-4 is responsible for node 5
CLUSTERIP Nodes:  3

....

[1 3]
backend-1 (me!) is responsible for node 1
backend-3 is responsible for node 2
backend-1 (me!) is responsible for node 3
backend-3 is responsible for node 4
backend-1 (me!) is responsible for node 5
CLUSTERIP Nodes:  1,3,5

Warning

Don't use this. It is just a proof-of-concept.

License

Apache2