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(Last edited by Jch on 21 Apr 2015.)

Consul

Introduction

This page is currently my experimental log about consul on AL.

Downloaded package: consul-0.5.0-r0.apk from http://repos.mauras.ch/alpinelinux/x86_64/

Will prepare 5 KVM: 3 consul server (in run-from-ram mode) and 2 consul agent (a SAN (NBD) and a LXC host in data mode) on an isolated network.

We will experiment to find the right spec to allocate the consul servers for 100 to 1000 agents.

We plan to orchestrate our VM fleet based on consul events, envconsul and consul-template. All with ash scripts and smart setup.

We combine our PXE servers and the consul ones to inherit from the consul resilence (consul leader) to offer high-availability (HA) (but still in ram only) to the PXE service.

Currently, we have scripts to adapt a freshly PXE booted machine into a

PXE and consul server
SAN (san.service.consul)
generic diskless machine (for KVM or services) (kvm.service.consul)
generic data mode machine (/var) (for LXC or services) (lxc.service.consul)
machine with physical drives (raid + KVM + SAN) (raid.service.consul; kvm.service.consul)
specific sys mode machine (sys.service.consul)

We have defined:

*.kvm.service.consul
*.lxc.service.consul
*.san.service.consul
*.nbd.service.consul
*.raid.service.consul
*.nas.service.consul
*.sys.service.consul
time.service.consul
repo.service.consul
resolver.service.consul
dns.service.consul
collectd.service.consul
webcache.service.consul
mariadb.service.consul
*.ldap.service.consul
relay.service.consul
syslog.service.consul
*.ceph.service.consul
*.git.service.consul
*.vpn.service.consul
etc

Install

We will just focus on the consul installation and configuration parts.

wget http://repos.mauras.ch/alpinelinux/x86_64/consul-0.5.0-r0.apk
apk add consul-0.5.0-r0.apk --allow-untrusted --force

Configuration

Consul v0.5.0
Consul Protocol: 2 (Understands back to: 1)

By default, there are 4 files in /etc/consul

acl.json.sample      encrypt.json.sample  server.json          tls.json.sample

Consul Server

As in our setup we want as many PXE server (in stand-by mode) than consul server, installing a consul server is done by a script doing

whoami on the LAN ?
find IP of boot server (is consul leader)
preconfigure OS
install package from stable
install package from edge
rsync data
install experimental consul package
start consul as server
untie from boot server
get ENV from consul
configure networking
start networking
start sshd
(restart consul?)
configure dnsmasq
start dnsmasq
configure ntpd
start ntpd
register time.service.consul
configure collectd
start collectd
configure dhcpd
configure pxelinux
start in.tftp
configure NFS
start NFS
configure darkhttpd
start darkhttpd
register repo.service.consul
register pxe.service.consul

dhcpd will be started manually for now but later by the consul leader election.

DNSmasq with consul

apk add dnsmasq
mkdir -p /etc/dnsmasq.d
echo "server=/consul/127.0.0.1#8600" > /etc/dnsmasq.d/10-consul
echo "resolv-file=/etc/resolv.dnsmasq" > /etc/dnsmasq.d/20-resolv
echo "nameserver ${DNS1}" > /etc/resolv.dnsmasq
echo "nameserver ${DNS2}" >> /etc/resolv.dnsmasq
echo <<EOF > /etc/conf.d/dnsmasq
MASQ_OPTS="--user=dnsmasq --group=dnsmasq --interface=eth0 --conf-dir=/etc/dnsmasq.d"
EOF
rc-service dnsmasq start

Consul Agent

We need to lauch the consul service after being able to read the IP address of the PXEserver involved.
This particuliar address will be used to join the consul cluster as agent.

whoami on the LAN ?
find IP of boot server (is consul leader)
preconfigure OS
install package from stable
install package from edge
install experimental consul package
get standard agent config
start consul as agent
join consul cluster
untie from boot server
get ENV from consul
configure dnsmasq
restart dnsmasq
configure collectd
start collectd

Whenever possible, a service will be referenced by its name (like collectd.service.consul for the collectd server).
Consul agent and dnsmasq are the 2 first services to be started on each machine.

Bootstrap the consul cluster

Is to launch the 3 first servers lying to them about the first consul server because we do not want to switch PXE production at the same time we are introducing consul...

We have scipts to adapt a freshly PXE launched machine to the role of:

PXE and consul server
SAN
generic diskless machine (for KVM or services)
generic data mode machine (/var) (for LXC or services)
machine with physical drives (raid + KVM + SAN)
specific sys mode machine (apkovl or -boot c)

Usage

Be sure to have proxt http disabled if you want to use curl against localhost...

Machines discovery

List machines =

consul members

or

curl localhost:8500/v1/catalog/nodes

list PXEservers = servers in "consul members"

get consul leader = ???

Services discovery

Register service =

echo '{"service": {"name": "pxe"}}' > /etc/consul/pxe.json ; consul reload

List services :

curl http://localhost:8500/v1/agent/services : Returns the services the local agent is managing 
curl http://localhost:8500/v1/catalog/services : Lists services in a given DC 
curl http://localhost:8500/v1/catalog/service/<service> : Lists the nodes in a given service
curl http://localhost:8500/v1/catalog/node/<node> : Lists the services provided by a node

What if ?

What if I register a service service1 with tag tag1 on node node1, then I register a service service1 with tag tag2 on node2. then I register a service service1 with tag tag3 on node1?

will the tags just add?

I plan to advertize available NBD with {"service": "nbd", "tags": ["<name>"]} ans access it with nbd:name.nbd.service.consul:name.

Cheks

Key/Value storage

curl -X PUT -d 'value' http://localhost:8500/v1/kv/path/to/key

curl http://localhost:8500/v1/kv/path/to/key

curl -X DELETE http://localhost:8500/v1/kv/path/to/key?recurse

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