# Ekka
Ekka - Autocluster and Autoheal for EMQ. Ekka helps build a new distribution layer for EMQ R2.3.
```
---------- ----------
| EMQX |<--- MQTT--->| EMQX |
|--------| |--------|
| Ekka |<----RPC---->| Ekka |
|--------| |--------|
| Mnesia |<--Cluster-->| Mnesia |
|--------| |--------|
| Kernel |<----TCP---->| Kernel |
---------- ----------
```
## Node discovery and Autocluster
Ekka supports erlang node discovery and autocluster using various strategies:
Strategy | Description
-----------|--------------------------------------
manual | Join cluster manually
static | Static node list
mcast | IP Multicast
dns | DNS A Records
etcd | etcd
k8s | Kubernetes
The configuration example files are under 'etc/' folder.
### Cluster using static node list
Erlang config:
```
{cluster_discovery,
{static, [
{seeds, ['ekka1@127.0.0.1', 'ekka2@127.0.0.1']}
]}},
```
Cuttlefish style config:
```
cluster.discovery = static
cluster.static.seeds = ekka1@127.0.0.1,ekka2@127.0.0.1
```
### Cluster using IP Multicast
Erlang config:
```
{cluster_discovery,
{mcast, [
{addr,{239,192,0,1}},
{ports,[4369,4370]},
{iface,{0,0,0,0}},
{ttl, 255},
{loop,true}
]}},
```
Cuttlefish style config:
```
cluster.discovery = mcast
## IP Multicast Address.
##
## Value: IP Address
cluster.mcast.addr = 239.192.0.1
## Multicast Ports.
##
## Value: Port List
cluster.mcast.ports = 4369,4370
## Multicast Iface.
##
## Value: Iface Address
##
## Default: 0.0.0.0
cluster.mcast.iface = 0.0.0.0
## Multicast Ttl.
##
## Value: 0-255
cluster.mcast.ttl = 255
## Multicast loop.
##
## Value: on | off
cluster.mcast.loop = on
```
### Cluster using DNS A records
Erlang Config:
```
{cluster_discovery,
{dns, [
{server, "http://127.0.0.1:2379"},
{prefix, "ekkacluster"},
{node_ttl, 60000}
]}},
```
Cuttlefish style config:
```
cluster.discovery = dns
## DNS name.
##
## Value: String
cluster.dns.name = localhost
## The App name is used to build 'node.name' with IP address.
##
## Value: String
cluster.dns.app = ekka
```
### Cluster using etcd
Erlang config:
```
{cluster_discovery,
{etcd, [
{server, ["http://127.0.0.1:2379"]},
{prefix, "ekkacluster"},
{node_ttl, 60000}
]}},
```
Cuttlefish style config:
```
cluster.discovery = etcd
## Etcd server list, seperated by ','.
##
## Value: String
cluster.etcd.server = http://127.0.0.1:2379
## The prefix helps build nodes path in etcd. Each node in the cluster
## will create a path in etcd: v2/keys/<prefix>/<cluster.name>/<node.name>
##
## Value: String
cluster.etcd.prefix = ekkacl
## The TTL for node's path in etcd.
##
## Value: Duration
##
## Default: 1m, 1 minute
cluster.etcd.node_ttl = 1m
```
### Cluster using Kubernates
Erlang Config:
```
{cluster_discovery,
{k8s, [
{apiserver, "http://10.110.111.204:8080"},
{app, ekka}
]}},
```
Cuttlefish style config:
```
cluster.discovery = k8s
## Kubernates API server list, seperated by ','.
##
## Value: String
cluster.k8s.apiserver = http://10.110.111.204:8080
## The service name helps lookup EMQ nodes in the cluster.
##
## Value: String
cluster.k8s.service_name = ekka
## The address type is used to extract host from k8s service.
##
## Value: ip | dns
cluster.k8s.address_type = ip
## The app name helps build 'node.name'.
##
## Value: String
cluster.k8s.app_name = ekka
```
## Network partition and Autoheal
### Autoheal Design
When network partition occurs, the following steps to heal the cluster if autoheal is enabled:
1. Node reports the partitions to a leader node which has the oldest guid.
2. Leader node create a global netsplit view and choose one node in the majority as coordinator.
3. Leader node requests the coordinator to autoheal the network partition.
4. Coordinator node reboots all the nodes in the minority side.
### Enable autoheal
Erlang config:
```
{cluster_autoheal, true},
```
Cuttlefish style config:
```
cluster.autoheal = on
```
## Node down and Autoclean
### Autoclean Design
A down node will be removed from the cluster if autoclean is enabled.
### Enable autoclean
Erlang config:
```
{cluster_autoclean, 60000},
```
Cuttlefish style config:
```
cluster.autoclean = 5m
```
## Lock Service
Ekka implements a simple distributed lock service in 0.3 release. The Lock APIs:
TODO:
## Cluster without epmd
The ekka 0.6.0 release implements erlang distribiton without epmd.
See: http://erlang.org/pipermail/erlang-questions/2015-December/087013.html
For example:
```
## Dist port: 4370
erl -pa ebin -pa _build/default/lib/*/ebin -proto_dist ekka -start_epmd false -epmd_module ekka_epmd -name node1@127.0.0.1 -s ekka
## Dist port: 4371
erl -pa ebin -pa _build/default/lib/*/ebin -proto_dist ekka -start_epmd false -epmd_module ekka_epmd -name node2@127.0.0.1 -s ekka
## Dist port: 4372
erl -pa ebin -pa _build/default/lib/*/ebin -proto_dist ekka -start_epmd false -epmd_module ekka_epmd -name node3@127.0.0.1 -s ekka
```
The erlang distribution port can be tuned by ekka `inet_dist_base_port` env. The default port is 4370.
## License
Apache License Version 2.0
## Author
EMQ X Team.