Kubernetes Virtual IP address/es using keepalived
AKA "how to set up virtual IP addresses in kubernetes using IPVS - The Linux Virtual Server Project".
There are 2 ways to expose a service in the current kubernetes service model:
- Create a cloud load balancer.
- Allocate a port (the same port) on every node in your cluster and proxy traffic through that port to the endpoints.
This just works. What's the issue then?
The issue is that it does not provide High Availability because beforehand is required to know the IP addresss of the node where is running and in case of a failure the pod can be be moved to a different node. Here is where ipvs could help. The idea is to define an IP address per service to expose it outside the Kubernetes cluster and use vrrp to announce this "mapping" in the local network. With 2 or more instance of the pod running in the cluster is possible to provide high availabity using a single IP address.
What is the difference between this and service-loadbalancer or nginx-alpha to expose one or more services?
This should be considered a complement, not a replacement for HAProxy or nginx. The goal using keepalived is to provide high availability and to bring certainty about how an exposed service can be reached (beforehand we know the ip address independently of the node where is running). For instance keepalived can use used to expose the service-loadbalancer or nginx ingress controller in the LAN using one IP address.
Daemonsets enabled is the only requirement. Check this guide with the required flags in kube-apiserver.
To expose one or more services use the flag services-configmap. The format of the data is: external IP -> namespace/serviceName. Optionally is possible to specify forwarding method using : after the service name. The valid options are NAT, DR and PROXY.
For instance external IP -> namespace/serviceName:DR.
If the method is not specified it will use NAT.
This IP must be routable inside the LAN and must be available. By default the IP address of the pods are used to route the traffic. This means that is one pod dies or a new one is created by a scale event the keepalived configuration file will be updated and reloaded.
First we create a new replication controller and service
$ kubectl create -f examples/echoheaders.yaml
replicationcontroller "echoheaders" created
You have exposed your service on an external port on all nodes in your
cluster. If you want to expose this service to the external internet, you may
need to set up firewall rules for the service port(s) (tcp:30302) to serve traffic.
See http://releases.k8s.io/HEAD/docs/user-guide/services-firewalls.md for more details.
service "echoheaders" created
Next add the required annotation to expose the service using a local IP
$ echo "apiVersion: v1
kind: ConfigMap
metadata:
name: vip-configmap
data:
10.4.0.50: default/echoheaders" | kubectl create -f -
Now the creation of the daemonset
$ kubectl create -f vip-daemonset.yaml
daemonset "kube-keepalived-vip" created
$ kubectl get daemonset
NAME CONTAINER(S) IMAGE(S) SELECTOR NODE-SELECTOR
kube-keepalived-vip kube-keepalived-vip aledbf/kube-keepalived-vip:0.15 name in (kube-keepalived-vip) type=worker
Note: the daemonset yaml file contains a node selector. This is not required, is just an example to show how is possible to limit the nodes where keepalived can run
To verify if everything is working we should check if a kube-keepalived-vip pod is in each node of the cluster
$ kubectl get nodes
NAME LABELS STATUS AGE
10.4.0.3 kubernetes.io/hostname=10.4.0.3,type=worker Ready 1d
10.4.0.4 kubernetes.io/hostname=10.4.0.4,type=worker Ready 1d
10.4.0.5 kubernetes.io/hostname=10.4.0.5,type=worker Ready 1d
$ kubectl get pods
NAME READY STATUS RESTARTS AGE
echoheaders-co4g4 1/1 Running 0 5m
kube-keepalived-vip-a90bt 1/1 Running 0 53s
kube-keepalived-vip-g3nku 1/1 Running 0 52s
kube-keepalived-vip-gd18l 1/1 Running 0 54s
$ kubectl logs kube-keepalived-vip-a90bt
I0410 14:24:45.860119 1 keepalived.go:161] cleaning ipvs configuration
I0410 14:24:45.873095 1 main.go:109] starting LVS configuration
I0410 14:24:45.894664 1 main.go:119] starting keepalived to announce VIPs
Starting Healthcheck child process, pid=17
Starting VRRP child process, pid=18
Initializing ipvs 2.6
Registering Kernel netlink reflector
Registering Kernel netlink reflector
Registering Kernel netlink command channel
Registering gratuitous ARP shared channel
Registering Kernel netlink command channel
Using LinkWatch kernel netlink reflector...
Using LinkWatch kernel netlink reflector...
I0410 14:24:56.017590 1 keepalived.go:151] reloading keepalived
Got SIGHUP, reloading checker configuration
Registering Kernel netlink reflector
Initializing ipvs 2.6
Registering Kernel netlink command channel
Registering gratuitous ARP shared channel
Registering Kernel netlink reflector
Opening file '/etc/keepalived/keepalived.conf'.
Registering Kernel netlink command channel
Opening file '/etc/keepalived/keepalived.conf'.
Using LinkWatch kernel netlink reflector...
VRRP_Instance(vips) Entering BACKUP STATE
Using LinkWatch kernel netlink reflector...
Activating healthchecker for service [10.2.68.5]:8080
VRRP_Instance(vips) Transition to MASTER STATE
VRRP_Instance(vips) Entering MASTER STATE
VRRP_Instance(vips) using locally configured advertisement interval (1000 milli-sec)
$ kubectl exec kube-keepalived-vip-a90bt cat /etc/keepalived/keepalived.conf
global_defs {
vrrp_version 3
vrrp_iptables KUBE-KEEPALIVED-VIP
}
vrrp_instance vips {
state BACKUP
interface eth1
virtual_router_id 50
priority 100
nopreempt
advert_int 1
track_interface {
eth1
}
virtual_ipaddress {
172.17.4.90
}
}
# Service: default/echoheaders
virtual_server 10.4.0.50 80 {
delay_loop 5
lvs_sched wlc
lvs_method NAT
persistence_timeout 1800
protocol TCP
real_server 10.2.68.5 8080 {
weight 1
TCP_CHECK {
connect_port 8080
connect_timeout 3
}
}
}
$ curl -v 10.4.0.50
* Rebuilt URL to: 10.4.0.50/
* Trying 10.4.0.50...
* Connected to 10.4.0.50 (10.4.0.50) port 80 (#0)
> GET / HTTP/1.1
> Host: 10.4.0.50
> User-Agent: curl/7.43.0
> Accept: */*
>
* HTTP 1.0, assume close after body
< HTTP/1.0 200 OK
< Server: BaseHTTP/0.6 Python/3.5.0
< Date: Wed, 30 Dec 2015 19:52:39 GMT
<
CLIENT VALUES:
client_address=('10.4.0.148', 52178) (10.4.0.148)
command=GET
path=/
real path=/
query=
request_version=HTTP/1.1
SERVER VALUES:
server_version=BaseHTTP/0.6
sys_version=Python/3.5.0
protocol_version=HTTP/1.0
HEADERS RECEIVED:
Accept=*/*
Host=10.4.0.50
User-Agent=curl/7.43.0
* Closing connection 0
Scaling the replication controller should update and reload keepalived
$ kubectl scale --replicas=5 replicationcontroller echoheaders
replicationcontroller "echoheaders" scaled
$ kubectl exec kube-keepalived-vip-a90bt cat /etc/keepalived/keepalived.conf
global_defs {
vrrp_version 3
vrrp_iptables KUBE-KEEPALIVED-VIP
}
vrrp_instance vips {
state BACKUP
interface eth1
virtual_router_id 50
priority 100
nopreempt
advert_int 1
track_interface {
eth1
}
virtual_ipaddress {
172.17.4.90
}
}
# Service: default/echoheaders
virtual_server 10.4.0.50 80 {
delay_loop 5
lvs_sched wlc
lvs_method NAT
persistence_timeout 1800
protocol TCP
real_server 10.2.68.5 8080 {
weight 1
TCP_CHECK {
connect_port 8080
connect_timeout 3
}
}
real_server 10.2.68.6 8080 {
weight 1
TCP_CHECK {
connect_port 8080
connect_timeout 3
}
}
real_server 10.2.68.7 8080 {
weight 1
TCP_CHECK {
connect_port 8080
connect_timeout 3
}
}
real_server 10.2.68.8 8080 {
weight 1
TCP_CHECK {
connect_port 8080
connect_timeout 3
}
}
real_server 10.2.68.9 8080 {
weight 1
TCP_CHECK {
connect_port 8080
connect_timeout 3
}
}
}
```
## PROXY Protocol mode
The [PROXY Protocol](http://haproxy.1wt.eu/download/1.6/doc/proxy-protocol.txt) allows the transport connection information such as a client's address across multiple layers of NAT or TCP. Usually this is information is lost, containing information about the last hop.
There is only one caveat using this protocol: the destination must "understand" the protocol. Without this is not possible to read the traffic.
To enable this feature the flag `--proxy-protocol-mode=true` is required.
**Using this flag implies that HAProxy will be responsible of handling the load balancing in TCP mode**
[HAProxy](http://haproxy.1wt.eu) is used to in conjunction win Keepalived so send proxy packets.
Example:
First create a configmap with the VIP mapping
```
echo "apiVersion: v1
data:
10.4.0.50: default/nginx-ingress-lb:PROXY
10.4.0.51: default/echoheaders
kind: ConfigMap
metadata:
name: vip-configmap
namespace: default" | kubectl create -f -
```
Where `default/nginx-ingress-lb` is a [NGINX Ingress controller](https://github.com/kubernetes/contrib/tree/master/ingress/controllers/nginx) with the option `use-proxy-protocol:true`.
The Ingress controller just have one rule using the [echoheaders]() container.
```
old-mbp:~ aledbf$ kubectl get ing
NAME RULE BACKEND ADDRESS AGE
default-server - 10.4.0.5 1d
/ echoheaders-x:80
```
```
kubectl create -f vip-daemonser-proxy.xml
```
Finally test the content of the header `x-forwarded-for` to verify it returns the IP address of the client
```
$ curl -v http://10.4.0.50
curl 10.4.0.50
CLIENT VALUES:
client_address=10.2.0.186
command=GET
real path=/
query=nil
request_version=1.1
request_uri=http://10.4.0.50:8080/
SERVER VALUES:
server_version=nginx: 1.9.7 - lua: 9019
HEADERS RECEIVED:
accept=*/*
connection=close
host=10.4.0.50
user-agent=curl/7.43.0
x-forwarded-for=10.4.0.148
x-forwarded-host=10.4.0.50
x-forwarded-port=80
x-forwarded-proto=http
x-real-ip=10.4.0.148
BODY:
-no body in request-
```
## Related projects
- https://github.com/kobolog/gorb
- https://github.com/qmsk/clusterf
- https://github.com/osrg/gobgp