Kubernetes requires a set of machines to host the Kubernetes control plane and the worker nodes where containers are ultimately run. In this lab you will provision the compute resources required for running a secure and highly available Kubernetes cluster.
The Kubernetes networking model assumes a flat network in which containers and nodes can communicate with each other. In cases where this is not desired network policies can limit how groups of containers are allowed to communicate with each other and external network endpoints.
Setting up network policies is out of scope for this tutorial.
The public network is a network that contains external access and can be reached by the outside world. The public network creation can be only done by an OpenStack administrator.
The following commands provide an example of creating an OpenStack provider network for public network access.
As an OpenStack administrator:
source /path/to/admin-rc
openstack network create \
--external \
--provider-network-type flat \
--provider-physical-network datacentre \
public_network
openstack subnet create \
--gateway <ip> \
--allocation-pool start=<float_start>,end=<float_end> \
--network public_network \
--subnet-range <CIDR> \
public_subnet
<float_start> and <float_end> are the associated floating IP pool provided to the network labeled public network. The Classless Inter-Domain Routing (CIDR) uses the format /<routing_prefix>, i.e. 10.5.2.1/24
The private tenant network is connected to the public network via a router during the network setup. This allows each OpenStack Platform instance attached to the internal network the ability to request a floating IP from the public network for public access.
Follow the OpenStack documentation for more information.
Create the kubernetes-the-hard-way private network:
openstack network create kubernetes-the-hard-way
The kubernetes-the-hard-way-router router:
openstack router create kubernetes-the-hard-way-router
A subnet must be provisioned with an IP address range large enough to assign a private IP address to each node in the Kubernetes cluster.
Create the kubernetes subnet in the kubernetes-the-hard-way network:
openstack subnet create --network kubernetes-the-hard-way \
--subnet-range 10.240.0.0/24 \
kubernetes
The
10.240.0.0/24IP address range can host up to 254 compute instances.
Once the subnet is created, the router should be configured as the default gateway
openstack router add subnet kubernetes-the-hard-way-router $(openstack subnet show kubernetes -f value -c id)
openstack router set \
--external-gateway $(openstack network show public_network -f value -c id) \
kubernetes-the-hard-way-router
Create a security group that allows internal communication across all protocols:
openstack security group create kubernetes-the-hard-way-allow-internal
for protocol in tcp udp icmp
do
openstack security group rule create \
--ingress \
--protocol ${protocol} \
--remote-group kubernetes-the-hard-way-allow-internal \
kubernetes-the-hard-way-allow-internal
done
Create a security group that allows external SSH, ICMP, and HTTPS:
openstack security group create kubernetes-the-hard-way-allow-external
openstack security group rule create \
--ingress \
--protocol icmp \
kubernetes-the-hard-way-allow-external
for port in 22 6443
do
openstack security group rule create \
--ingress \
--protocol tcp \
--dst-port ${port} \
kubernetes-the-hard-way-allow-external
done
List the security groups:
openstack security group list -f table -c ID -c Name
output
+--------------------------------------+----------------------------------------+
| ID | Name |
+--------------------------------------+----------------------------------------+
| 074fd87a-ca28-4eb2-8abb-babe039fb739 | kubernetes-the-hard-way-allow-internal |
| b25f2854-fac7-4227-b9bc-00d83fb295cf | default |
| e4d6d4ea-dfdb-4e78-809f-c37b2cef7d91 | kubernetes-the-hard-way-allow-external |
+--------------------------------------+----------------------------------------+
To be able to create instances, an image should be provided. Depending on the OpenStack environment an image catalog can be provided. In this guide we will use CentOS 7 as the base operating system. Follow the next steps to upload a new CentOS 7 image:
Download the latest CentOS 7 Generic Cloud image (at the time of writing this guide, 1907)
wget http://cloud.centos.org/centos/7/images/CentOS-7-x86_64-GenericCloud-1907.raw.tar.gz
tar xzvf CentOS-7-x86_64-GenericCloud-1907.raw.tar.gz
Upload it to the Glance service:
openstack image create CentOS-7-x86_64-GenericCloud-1907 \
--disk-format=raw \
--container-format=bare < CentOS-7-x86_64-GenericCloud-1907.raw
Optionally, clean up the downloaded files:
rm -f CentOS-7-x86_64-GenericCloud-1907.raw CentOS-7-x86_64-GenericCloud-1907.raw.tar.gz
It is required to have a proper DNS configuration. If not using DNSaaS, you can create an instance and setup a proper DNS following the next instructions.
Create a security group to allow DNS communication within the internal network:
openstack security group create kubernetes-the-hard-way-allow-dns
openstack security group rule create \
--ingress \
--protocol icmp \
kubernetes-the-hard-way-allow-dns
openstack security group rule create \
--ingress \
--protocol tcp \
--dst-port 22 \
kubernetes-the-hard-way-allow-dns
for PROTO in udp tcp;
do
openstack security group rule create \
--ingress \
--protocol $PROTO \
--dst-port 53 \
--remote-ip 10.240.0.0/24 \
kubernetes-the-hard-way-allow-dns;
done
Create an instance to host the DNS service. In this case the CentOS image is used.
DOMAIN="k8s.lan"
openstack server create \
--nic net-id=$(openstack network show kubernetes-the-hard-way -f value -c id),v4-fixed-ip=10.240.0.100 \
--security-group=kubernetes-the-hard-way-allow-dns \
--flavor m1.small \
--image CentOS-7-x86_64-GenericCloud-1907 \
--key-name k8s-the-hard-way \
dns.${DOMAIN}
Add a floating ip to make it reachable externally:
openstack server add floating ip dns.${DOMAIN} $(openstack floating ip create public_network --description dns -f value -c floating_ip_address)
The domain used in this guide is configured to be k8s.lan.
The following steps shows how to install a DNS service using named in the instance previously created.
First, connect to the instance:
DNS_EXTERNAL_IP=$(openstack server show dns.${DOMAIN} -f value -c addresses | awk '{ print $2 }')
ssh -i ~/.ssh/k8s.pem centos@${DNS_EXTERNAL_IP}
Configure network resolution and install named:
DOMAIN="k8s.lan"
UPSTREAM_DNS=$(awk '/nameserver/ { print $2 }' /etc/resolv.conf | head -n1)
sudo tee -a /etc/sysconfig/network-scripts/ifcfg-eth0 << EOF
DNS1=${UPSTREAM_DNS}
PEERDNS=no
EOF
sudo yum install -y firewalld python-firewall bind-utils bind
sudo systemctl enable firewalld --now
sudo firewall-cmd --zone public --add-service dns
sudo firewall-cmd --zone public --add-service dns --permanent
sudo cp /etc/named.conf{,.orig}
sudo tee /etc/named.conf << EOF
options {
listen-on port 53 { any; };
directory "/var/named";
dump-file "/var/named/data/cache_dump.db";
statistics-file "/var/named/data/named_stats.txt";
memstatistics-file "/var/named/data/named_mem_stats.txt";
allow-query { any; };
forward only;
forwarders { ${UPSTREAM_DNS}; };
managed-keys-directory "/var/named/dynamic";
pid-file "/run/named/named.pid";
session-keyfile "/run/named/session.key";
};
logging {
channel default_debug {
file "data/named.run";
severity dynamic;
};
};
zone "." IN {
type hint;
file "named.ca";
};
include "/etc/named.rfc1912.zones";
include "/etc/named.root.key";
include "/etc/named/zones.conf";
EOF
sudo tee /etc/named/zones.conf << EOF
include "/etc/named/update.key" ;
zone ${DOMAIN} {
type master ;
file "/var/named/dynamic/zone.db" ;
allow-update { key update-key ; } ;
};
EOF
sudo rndc-confgen -a -c /etc/named/update.key -k update-key -r /dev/urandom
sudo chown root.named /etc/named/update.key
sudo chmod 640 /etc/named/update.key
INTERNAL_IP=$(curl -s http://169.254.169.254/latest/meta-data/local-ipv4)
sudo tee /var/named/dynamic/zone.db << EOF
\$ORIGIN .
\$TTL 300 ; 5 minutes
${DOMAIN} IN SOA dns.${DOMAIN}. admin.${DOMAIN}. (
1 ; serial
28800 ; refresh (8 hours)
3600 ; retry (1 hour)
604800 ; expire (1 week)
86400 ; minimum (1 day)
)
NS dns.${DOMAIN}.
\$ORIGIN ${DOMAIN}.
\$TTL 3600 ; 1 hour
dns A ${INTERNAL_IP}
k8sosp A 10.240.0.200
controller-0 A 10.240.0.10
controller-1 A 10.240.0.11
controller-2 A 10.240.0.12
worker-0 A 10.240.0.20
worker-1 A 10.240.0.21
worker-2 A 10.240.0.22
EOF
Verify everything is properly configured:
sudo named-checkconf /etc/named.conf
sudo named-checkzone ${DOMAIN} /var/named/dynamic/zone.db
Start and enable the named service:
sudo systemctl enable named --now
Verify it is working
dig @${INTERNAL_IP} ${DOMAIN} axfr
output
; <<>> DiG 9.11.4-P2-RedHat-9.11.4-9.P2.el7 <<>> @10.240.0.100 k8s.lan axfr
; (1 server found)
;; global options: +cmd
k8s.lan. 300 IN SOA dns.k8s.lan. admin.k8s.lan. 1 28800 3600 604800 86400
k8s.lan. 300 IN NS dns.k8s.lan.
controller-0.k8s.lan. 3600 IN A 10.240.0.10
controller-1.k8s.lan. 3600 IN A 10.240.0.11
controller-2.k8s.lan. 3600 IN A 10.240.0.12
dns.k8s.lan. 3600 IN A 10.240.0.100
k8sosp.k8s.lan. 3600 IN A 10.240.0.200
worker-0.k8s.lan. 3600 IN A 10.240.0.20
worker-1.k8s.lan. 3600 IN A 10.240.0.21
worker-2.k8s.lan. 3600 IN A 10.240.0.22
k8s.lan. 300 IN SOA dns.k8s.lan. admin.k8s.lan. 1 28800 3600 604800 86400
;; Query time: 1 msec
;; SERVER: 10.240.0.100#53(10.240.0.100)
;; WHEN: mié sep 25 10:22:04 UTC 2019
;; XFR size: 10 records (messages 1, bytes 310)
Finally, update all packages to latest version and reboot the instance just in case:
sudo yum clean all
sudo yum update -y
sudo reboot
After installing the DNS service, modify the private subnet to use that DNS service:
DOMAIN="k8s.lan"
DNS_INTERNAL_IP=$(openstack server show dns.${DOMAIN} -f value -c addresses | awk -F'[=,]' '{print $2}')
openstack subnet set --dns-nameserver ${DNS_INTERNAL_IP} kubernetes
In order to have a proper Kubernetes high available environment, a Load balancer is required to distribute the API load. If not using LBaaS, you can create an instance and setup a proper Load balancer following the next instructions.
Create an instance to host the load balancer service. In this case the CentOS image is used.
DOMAIN="k8s.lan"
openstack server create \
--nic net-id=$(openstack network show kubernetes-the-hard-way -f value -c id),v4-fixed-ip=10.240.0.200 \
--security-group kubernetes-the-hard-way-allow-internal \
--security-group kubernetes-the-hard-way-allow-external \
--flavor m1.small \
--image CentOS-7-x86_64-GenericCloud-1907 \
--key-name k8s-the-hard-way \
k8sosp.${DOMAIN}
Add a floating ip to make it reachable externally:
openstack server add floating ip k8sosp.${DOMAIN} $(openstack floating ip create public_network --description k8s-lb -f value -c floating_ip_address)
The following steps shows how to install a load balancer service using HAProxy in the instance previously created.
First, connect to the instance:
LB_EXTERNAL_IP=$(openstack server show k8sosp.${DOMAIN} -f value -c addresses | awk '{ print $2 }')
ssh -i ~/.ssh/k8s.pem centos@${LB_EXTERNAL_IP}
Install and configure HAProxy:
DOMAIN="k8s.lan"
sudo yum install -y haproxy
sudo tee /etc/haproxy/haproxy.cfg << EOF
global
log 127.0.0.1 local2
chroot /var/lib/haproxy
pidfile /var/run/haproxy.pid
maxconn 4000
user haproxy
group haproxy
daemon
stats socket /var/lib/haproxy/stats
defaults
log global
option httplog
option dontlognull
option http-server-close
option redispatch
retries 3
timeout http-request 10s
timeout queue 1m
timeout connect 10s
timeout client 1m
timeout server 1m
timeout http-keep-alive 10s
timeout check 10s
maxconn 3000
listen stats :9000
stats enable
stats realm Haproxy\ Statistics
stats uri /haproxy_stats
stats auth admin:password
stats refresh 30
mode http
frontend main *:6443
default_backend mgmt6443
option tcplog
backend mgmt6443
balance source
mode tcp
# MASTERS 6443
server controller-0.${DOMAIN} 10.240.0.10:6443 check
server controller-1.${DOMAIN} 10.240.0.11:6443 check
server controller-2.${DOMAIN} 10.240.0.12:6443 check
EOF
As the Kubernetes port is 6443, the selinux policy should be modified to allow haproxy to listen on that particular port:
sudo semanage port --add --type http_port_t --proto tcp 6443
Verify everything is properly configured:
haproxy -c -V -f /etc/haproxy/haproxy.cfg
Start and enable the service
sudo systemctl enable haproxy --now
Finally, update all packages to latest version and reboot the instance just in case:
sudo yum clean all
sudo yum update -y
sudo reboot
Each compute instance will be provisioned with a fixed private IP address to simplify the Kubernetes bootstrapping process.
Create three compute instances which will host the Kubernetes control plane:
DOMAIN="k8s.lan"
for i in 0 1 2;
do
openstack server create \
--nic net-id=$(openstack network show kubernetes-the-hard-way -f value -c id),v4-fixed-ip=10.240.0.1${i} \
--flavor m1.medium \
--image CentOS-7-x86_64-GenericCloud-1907 \
--key-name k8s-the-hard-way \
--security-group kubernetes-the-hard-way-allow-external \
--security-group kubernetes-the-hard-way-allow-internal \
controller-${i}.${DOMAIN};
openstack server add floating ip controller-${i}.${DOMAIN} $(openstack floating ip create public_network -f value -c floating_ip_address)
done
Create three compute instances which will host the Kubernetes worker nodes:
DOMAIN="k8s.lan"
for i in 0 1 2;
do
openstack server create \
--nic net-id=$(openstack network show kubernetes-the-hard-way -f value -c id),v4-fixed-ip=10.240.0.2${i} \
--flavor m1.medium \
--image CentOS-7-x86_64-GenericCloud-1907 \
--key-name k8s-the-hard-way \
--security-group kubernetes-the-hard-way-allow-external \
--security-group kubernetes-the-hard-way-allow-internal \
worker-${i}.${DOMAIN};
openstack server add floating ip worker-${i}.${DOMAIN} $(openstack floating ip create public_network -f value -c floating_ip_address)
done
List the compute instances:
openstack server list -f table -c Name -c Networks -c Flavor -c Status
output
+----------------------+--------+-----------------------------------------------+-----------+
| Name | Status | Networks | Flavor |
+----------------------+--------+-----------------------------------------------+-----------+
| worker-2.k8s.lan | ACTIVE | kubernetes-the-hard-way=10.240.0.22, X.X.X.X | m1.medium |
| worker-1.k8s.lan | ACTIVE | kubernetes-the-hard-way=10.240.0.21, X.X.X.X | m1.medium |
| worker-0.k8s.lan | ACTIVE | kubernetes-the-hard-way=10.240.0.20, X.X.X.X | m1.medium |
| controller-2.k8s.lan | ACTIVE | kubernetes-the-hard-way=10.240.0.12, X.X.X.X | m1.medium |
| controller-1.k8s.lan | ACTIVE | kubernetes-the-hard-way=10.240.0.11, X.X.X.X | m1.medium |
| controller-0.k8s.lan | ACTIVE | kubernetes-the-hard-way=10.240.0.10, X.X.X.X | m1.medium |
| k8sosp.k8s.lan | ACTIVE | kubernetes-the-hard-way=10.240.0.200, X.X.X.X | m1.small |
| dns.k8s.lan | ACTIVE | kubernetes-the-hard-way=10.240.0.100, X.X.X.X | m1.small |
+----------------------+--------+-----------------------------------------------+-----------+
As the DNS server is created internally, it is a good idea to configure an external DNS server to use the public IPs to avoid using IPs to connect to the instances.
In this case for the sake of simplicity, we are using the local /etc/hosts in the local workstation:
openstack server list -f value -c Networks -c Name | sed -e 's/kubernetes-the-hard-way=.*, //g' | awk ' { t = $1; $1 = $2; $2 = t; print; } ' | sudo tee -a /etc/hosts
SSH will be used to configure the controller and worker instances. The openstack create command contained a specific ssh key that has been generated
previously and has been injected in the instances in order to be able to
connect to them without any password prompt.
To avoid asking to add the key to the ~/.ssh/known_hosts file, the following
snippet will do this up front:
for host in $(openstack server list -f value -c Name); do
ssh-keyscan -H ${host} >> ~/.ssh/known_hosts
done