Chapter 4. Replacing a master host
You can replace a failed master host.
First, remove the failed master host from your cluster, and then add a replacement master host. If the failed master host ran etcd, scale up etcd by adding etcd to the new master host.
You must complete all sections of this topic.
4.1. Deprecating a master host
Master hosts run important services, such as the OpenShift Container Platform API and controllers services. In order to deprecate a master host, these services must be stopped.
The OpenShift Container Platform API service is an active/active service, so stopping the service does not affect the environment as long as the requests are sent to a separate master server. However, the OpenShift Container Platform controllers service is an active/passive service, where the services leverage etcd to decide the active master.
Deprecating a master host in a multi-master architecture includes removing the master from the load balancer pool to avoid new connections attempting to use that master. This process depends heavily on the load balancer used. The steps below show the details of removing the master from haproxy
. In the event that OpenShift Container Platform is running on a cloud provider, or using a F5
appliance, see the specific product documents to remove the master from rotation.
Procedure
Remove the
backend
section in the/etc/haproxy/haproxy.cfg
configuration file. For example, if deprecating a master namedmaster-0.example.com
usinghaproxy
, ensure the host name is removed from the following:backend mgmt8443 balance source mode tcp # MASTERS 8443 server master-1.example.com 192.168.55.12:8443 check server master-2.example.com 192.168.55.13:8443 check
Then, restart the
haproxy
service.$ sudo systemctl restart haproxy
Once the master is removed from the load balancer, disable the API and controller services:
$ sudo systemctl disable --now atomic-openshift-master-api $ sudo systemctl disable --now atomic-openshift-master-controllers
- Because the master host is a unschedulable OpenShift Container Platform node, follow the steps in the Deprecating a node host section.
Remove the master host from the
[masters]
and[nodes]
groups in the/etc/ansible/hosts
Ansible inventory file to avoid issues if running any Ansible tasks using that inventory file.WarningDeprecating the first master host listed in the Ansible inventory file requires extra precautions.
The
/etc/origin/master/ca.serial.txt
file is generated on only the first master listed in the Ansible host inventory. If you deprecate the first master host, copy the/etc/origin/master/ca.serial.txt
file to the rest of master hosts before the process.The
kubernetes
service includes the master host IPs as endpoints. To verify that the master has been properly deprecated, review thekubernetes
service output and see if the deprecated master has been removed:$ oc describe svc kubernetes -n default Name: kubernetes Namespace: default Labels: component=apiserver provider=kubernetes Annotations: <none> Selector: <none> Type: ClusterIP IP: 10.111.0.1 Port: https 443/TCP Endpoints: 192.168.55.12:8443,192.168.55.13:8443 Port: dns 53/UDP Endpoints: 192.168.55.12:8053,192.168.55.13:8053 Port: dns-tcp 53/TCP Endpoints: 192.168.55.12:8053,192.168.55.13:8053 Session Affinity: ClientIP Events: <none>
After the master has been successfully deprecated, the host where the master was previously running can be safely deleted.
4.2. Adding hosts
You can add new hosts to your cluster by running the scaleup.yml playbook. This playbook queries the master, generates and distributes new certificates for the new hosts, and then runs the configuration playbooks on only the new hosts. Before running the scaleup.yml playbook, complete all prerequisite host preparation steps.
The scaleup.yml playbook configures only the new host. It does not update NO_PROXY in master services, and it does not restart master services.
You must have an existing inventory file,for example /etc/ansible/hosts, that is representative of your current cluster configuration in order to run the scaleup.yml playbook. If you previously used the atomic-openshift-installer
command to run your installation, you can check ~/.config/openshift/hosts for the last inventory file that the installer generated and use that file as your inventory file. You can modify this file as required. You must then specify the file location with -i
when you run the ansible-playbook
.
See the cluster limits section for the recommended maximum number of nodes.
Procedure
Ensure you have the latest playbooks by updating the atomic-openshift-utils package:
# yum update atomic-openshift-utils
Edit your /etc/ansible/hosts file and add new_<host_type> to the [OSEv3:children] section:
For example, to add a new node host, add new_nodes:
[OSEv3:children] masters nodes new_nodes
To add new master hosts, add new_masters.
Create a [new_<host_type>] section to specify host information for the new hosts. Format this section like an existing section, as shown in the following example of adding a new node:
[nodes] master[1:3].example.com node1.example.com openshift_node_labels="{'region': 'primary', 'zone': 'east'}" node2.example.com openshift_node_labels="{'region': 'primary', 'zone': 'west'}" infra-node1.example.com openshift_node_labels="{'region': 'infra', 'zone': 'default'}" infra-node2.example.com openshift_node_labels="{'region': 'infra', 'zone': 'default'}" [new_nodes] node3.example.com openshift_node_labels="{'region': 'primary', 'zone': 'west'}"
See Configuring Host Variables for more options.
When adding new masters, add hosts to both the [new_masters] section and the [new_nodes] section to ensure that the new master host is part of the OpenShift SDN.
[masters] master[1:2].example.com [new_masters] master3.example.com [nodes] master[1:2].example.com node1.example.com openshift_node_labels="{'region': 'primary', 'zone': 'east'}" node2.example.com openshift_node_labels="{'region': 'primary', 'zone': 'west'}" infra-node1.example.com openshift_node_labels="{'region': 'infra', 'zone': 'default'}" infra-node2.example.com openshift_node_labels="{'region': 'infra', 'zone': 'default'}" [new_nodes] master3.example.com
ImportantIf you label a master host with the
region=infra
label and have no other dedicated infrastructure nodes, you must also explicitly mark the host as schedulable by addingopenshift_schedulable=true
to the entry. Otherwise, the registry and router pods cannot be placed anywhere.Run the scaleup.yml playbook. If your inventory file is located somewhere other than the default of /etc/ansible/hosts, specify the location with the
-i
option.For additional nodes:
# ansible-playbook [-i /path/to/file] \ /usr/share/ansible/openshift-ansible/playbooks/byo/openshift-node/scaleup.yml
For additional masters:
# ansible-playbook [-i /path/to/file] \ /usr/share/ansible/openshift-ansible/playbooks/byo/openshift-master/scaleup.yml
- After the playbook runs, verify the installation.
Move any hosts that you defined in the [new_<host_type>] section to their appropriate section. By moving these hosts, subsequent playbook runs that use this inventory file treat the nodes correctly. You can keep the empty [new_<host_type>] section. For example, when adding new nodes:
[nodes] master[1:3].example.com node1.example.com openshift_node_labels="{'region': 'primary', 'zone': 'east'}" node2.example.com openshift_node_labels="{'region': 'primary', 'zone': 'west'}" node3.example.com openshift_node_labels="{'region': 'primary', 'zone': 'west'}" infra-node1.example.com openshift_node_labels="{'region': 'infra', 'zone': 'default'}" infra-node2.example.com openshift_node_labels="{'region': 'infra', 'zone': 'default'}" [new_nodes]
4.3. Scaling etcd
You can scale the etcd cluster vertically by adding more resources to the etcd hosts or horizontally by adding more etcd hosts.
Due to the voting system etcd uses, the cluster must always contain an odd number of members.
Having a cluster with an odd number of etcd hosts can account for fault tolerance. Having an odd number of etcd hosts does not change the number needed for a quorum but increases the tolerance for failure. For example, with a cluster of three members, quorum is two, which leaves a failure tolerance of one. This ensures the cluster continues to operate if two of the members are healthy.
Having an in-production cluster of three etcd hosts is recommended.
The new host requires a fresh Red Hat Enterprise Linux version 7 dedicated host. The etcd storage should be located on an SSD disk to achieve maximum performance and on a dedicated disk mounted in /var/lib/etcd
.
Prerequisites
- Before you add a new etcd host, perform a backup of both etcd configuration and data to prevent data loss.
Check the current etcd cluster status to avoid adding new hosts to an unhealthy cluster.
If you use the v2 etcd api, run this command:
# etcdctl --cert-file=/etc/etcd/peer.crt \ --key-file=/etc/etcd/peer.key \ --ca-file=/etc/etcd/ca.crt \ --peers="https://*master-0.example.com*:2379,\ https://*master-1.example.com*:2379,\ https://*master-2.example.com*:2379"\ cluster-health member 5ee217d19001 is healthy: got healthy result from https://192.168.55.12:2379 member 2a529ba1840722c0 is healthy: got healthy result from https://192.168.55.8:2379 member ed4f0efd277d7599 is healthy: got healthy result from https://192.168.55.13:2379 cluster is healthy
If you use the v3 etcd api, run this command:
# ETCDCTL_API=3 etcdctl --cert="/etc/etcd/peer.crt" \ --key=/etc/etcd/peer.key \ --cacert="/etc/etcd/ca.crt" \ --endpoints="https://*master-0.example.com*:2379,\ https://*master-1.example.com*:2379,\ https://*master-2.example.com*:2379" endpoint health https://master-0.example.com:2379 is healthy: successfully committed proposal: took = 5.011358ms https://master-1.example.com:2379 is healthy: successfully committed proposal: took = 1.305173ms https://master-2.example.com:2379 is healthy: successfully committed proposal: took = 1.388772ms
Before running the
scaleup
playbook, ensure the new host is registered to the proper Red Hat software channels:# subscription-manager register \ --username=*<username>* --password=*<password>* # subscription-manager attach --pool=*<poolid>* # subscription-manager repos --disable="*" # subscription-manager repos \ --enable=rhel-7-server-rpms \ --enable=rhel-7-server-extras-rpms
etcd is hosted in the
rhel-7-server-extras-rpms
software channel.Upgrade etcd and iptables on the current etcd nodes:
# yum update etcd iptables-services
- Back up the /etc/etcd configuration for the etcd hosts.
- If the new etcd members will also be OpenShift Container Platform nodes, add the desired number of hosts to the cluster.
- The rest of this procedure assumes you added one host, but if you add multiple hosts, perform all steps on each host.
4.3.1. Adding a new etcd host using Ansible
Procedure
In the Ansible inventory file, create a new group named
[new_etcd]
and add the new host. Then, add thenew_etcd
group as a child of the[OSEv3]
group:[OSEv3:children] masters nodes etcd new_etcd 1 ... [OUTPUT ABBREVIATED] ... [etcd] master-0.example.com master-1.example.com master-2.example.com [new_etcd] 2 etcd0.example.com 3
From the host that installed OpenShift Container Platform and hosts the Ansible inventory file, run the etcd
scaleup
playbook:$ ansible-playbook /usr/share/ansible/openshift-ansible/playbooks/byo/openshift-etcd/scaleup.yml
After the playbook runs, modify the inventory file to reflect the current status by moving the new etcd host from the
[new_etcd]
group to the[etcd]
group:[OSEv3:children] masters nodes etcd new_etcd ... [OUTPUT ABBREVIATED] ... [etcd] master-0.example.com master-1.example.com master-2.example.com etcd0.example.com
If you use Flannel, modify the
flanneld
service configuration on every OpenShift Container Platform host, located at/etc/sysconfig/flanneld
, to include the new etcd host:FLANNEL_ETCD_ENDPOINTS=https://master-0.example.com:2379,https://master-1.example.com:2379,https://master-2.example.com:2379,https://etcd0.example.com:2379
Restart the
flanneld
service:# systemctl restart flanneld.service
4.3.2. Manually adding a new etcd host
Procedure
Modify the current etcd cluster
To create the etcd certificates, run the openssl
command, replacing the values with those from your environment.
Create some environment variables:
export NEW_ETCD_HOSTNAME="*etcd0.example.com*" export NEW_ETCD_IP="192.168.55.21" export CN=$NEW_ETCD_HOSTNAME export SAN="IP:${NEW_ETCD_IP}, DNS:${NEW_ETCD_HOSTNAME}" export PREFIX="/etc/etcd/generated_certs/etcd-$CN/" export OPENSSLCFG="/etc/etcd/ca/openssl.cnf"
NoteThe custom
openssl
extensions used asetcd_v3_ca_*
include the $SAN environment variable assubjectAltName
. See/etc/etcd/ca/openssl.cnf
for more information.Create the directory to store the configuration and certificates:
# mkdir -p ${PREFIX}
Create the server certificate request and sign it: (server.csr and server.crt)
# openssl req -new -config ${OPENSSLCFG} \ -keyout ${PREFIX}server.key \ -out ${PREFIX}server.csr \ -reqexts etcd_v3_req -batch -nodes \ -subj /CN=$CN # openssl ca -name etcd_ca -config ${OPENSSLCFG} \ -out ${PREFIX}server.crt \ -in ${PREFIX}server.csr \ -extensions etcd_v3_ca_server -batch
Create the peer certificate request and sign it: (peer.csr and peer.crt)
# openssl req -new -config ${OPENSSLCFG} \ -keyout ${PREFIX}peer.key \ -out ${PREFIX}peer.csr \ -reqexts etcd_v3_req -batch -nodes \ -subj /CN=$CN # openssl ca -name etcd_ca -config ${OPENSSLCFG} \ -out ${PREFIX}peer.crt \ -in ${PREFIX}peer.csr \ -extensions etcd_v3_ca_peer -batch
Copy the current etcd configuration and
ca.crt
files from the current node as examples to modify later:# cp /etc/etcd/etcd.conf ${PREFIX} # cp /etc/etcd/ca.crt ${PREFIX}
While still on the surviving etcd host, add the new host to the cluster. To add additional etcd members to the cluster, you must first adjust the default localhost peer in the
peerURLs
value for the first member:Get the member ID for the first member using the
member list
command:# etcdctl --cert-file=/etc/etcd/peer.crt \ --key-file=/etc/etcd/peer.key \ --ca-file=/etc/etcd/ca.crt \ --peers="https://172.18.1.18:2379,https://172.18.9.202:2379,https://172.18.0.75:2379" \ 1 member list
- 1
- Ensure that you specify the URLs of only active etcd members in the
--peers
parameter value.
Obtain the IP address where etcd listens for cluster peers:
$ ss -l4n | grep 2380
Update the value of
peerURLs
using theetcdctl member update
command by passing the member ID and IP address obtained from the previous steps:# etcdctl --cert-file=/etc/etcd/peer.crt \ --key-file=/etc/etcd/peer.key \ --ca-file=/etc/etcd/ca.crt \ --peers="https://172.18.1.18:2379,https://172.18.9.202:2379,https://172.18.0.75:2379" \ member update 511b7fb6cc0001 https://172.18.1.18:2380
-
Re-run the
member list
command and ensure the peer URLs no longer include localhost.
Add the new host to the etcd cluster. Note that the new host is not yet configured, so the status stays as
unstarted
until the you configure the new host.WarningYou must add each member and bring it online one at a time. When you add each additional member to the cluster, you must adjust the
peerURLs
list for the current peers. ThepeerURLs
list grows by one for each member added. Theetcdctl member add
command outputs the values that you must set in the etcd.conf file as you add each member, as described in the following instructions.# etcdctl -C https://${CURRENT_ETCD_HOST}:2379 \ --ca-file=/etc/etcd/ca.crt \ --cert-file=/etc/etcd/peer.crt \ --key-file=/etc/etcd/peer.key member add ${NEW_ETCD_HOSTNAME} https://${NEW_ETCD_IP}:2380 1 Added member named 10.3.9.222 with ID 4e1db163a21d7651 to cluster ETCD_NAME="<NEW_ETCD_HOSTNAME>" ETCD_INITIAL_CLUSTER="<NEW_ETCD_HOSTNAME>=https://<NEW_HOST_IP>:2380,<CLUSTERMEMBER1_NAME>=https:/<CLUSTERMEMBER2_IP>:2380,<CLUSTERMEMBER2_NAME>=https:/<CLUSTERMEMBER2_IP>:2380,<CLUSTERMEMBER3_NAME>=https:/<CLUSTERMEMBER3_IP>:2380" ETCD_INITIAL_CLUSTER_STATE="existing"
- 1
- In this line,
10.3.9.222
is a label for the etcd member. You can specify the host name, IP address, or a simple name.
Update the sample
${PREFIX}/etcd.conf
file.Replace the following values with the values generated in the previous step:
- ETCD_NAME
- ETCD_INITIAL_CLUSTER
- ETCD_INITIAL_CLUSTER_STATE
Modify the following variables with the new host IP from the output of the previous step. You can use
${NEW_ETCD_IP}
as the value.ETCD_LISTEN_PEER_URLS ETCD_LISTEN_CLIENT_URLS ETCD_INITIAL_ADVERTISE_PEER_URLS ETCD_ADVERTISE_CLIENT_URLS
- If you previously used the member system as an etcd node, you must overwrite the current values in the /etc/etcd/etcd.conf file.
Check the file for syntax errors or missing IP addresses, otherwise the etcd service might fail:
# vi ${PREFIX}/etcd.conf
-
On the node that hosts the installation files, update the
[etcd]
hosts group in the /etc/ansible/hosts inventory file. Remove the old etcd hosts and add the new ones. Create a
tgz
file that contains the certificates, the sample configuration file, and theca
and copy it to the new host:# tar -czvf /etc/etcd/generated_certs/${CN}.tgz -C ${PREFIX} . # scp /etc/etcd/generated_certs/${CN}.tgz ${CN}:/tmp/
Modify the new etcd host
Install
iptables-services
to provide iptables utilities to open the required ports for etcd:# yum install -y iptables-services
Create the
OS_FIREWALL_ALLOW
firewall rules to allow etcd to communicate:- Port 2379/tcp for clients
Port 2380/tcp for peer communication
# systemctl enable iptables.service --now # iptables -N OS_FIREWALL_ALLOW # iptables -t filter -I INPUT -j OS_FIREWALL_ALLOW # iptables -A OS_FIREWALL_ALLOW -p tcp -m state --state NEW -m tcp --dport 2379 -j ACCEPT # iptables -A OS_FIREWALL_ALLOW -p tcp -m state --state NEW -m tcp --dport 2380 -j ACCEPT # iptables-save | tee /etc/sysconfig/iptables
NoteIn this example, a new chain
OS_FIREWALL_ALLOW
is created, which is the standard naming the OpenShift Container Platform installer uses for firewall rules.WarningIf the environment is hosted in an IaaS environment, modify the security groups for the instance to allow incoming traffic to those ports as well.
Install etcd:
# yum install -y etcd
Ensure version
etcd-2.3.7-4.el7.x86_64
or greater is installed,Ensure the etcd service is not running:
# systemctl disable etcd --now
Remove any etcd configuration and data:
# rm -Rf /etc/etcd/* # rm -Rf /var/lib/etcd/*
Extract the certificates and configuration files:
# tar xzvf /tmp/etcd0.example.com.tgz -C /etc/etcd/
Modify the file ownership permissions:
# chown -R etcd/etcd /etc/etcd/* # chown -R etcd/etcd /var/lib/etcd/
Start etcd on the new host:
# systemctl enable etcd --now
Verify that the host is part of the cluster and the current cluster health:
If you use the v2 etcd api, run the following command:
# etcdctl --cert-file=/etc/etcd/peer.crt \ --key-file=/etc/etcd/peer.key \ --ca-file=/etc/etcd/ca.crt \ --peers="https://*master-0.example.com*:2379,\ https://*master-1.example.com*:2379,\ https://*master-2.example.com*:2379,\ https://*etcd0.example.com*:2379"\ cluster-health member 5ee217d19001 is healthy: got healthy result from https://192.168.55.12:2379 member 2a529ba1840722c0 is healthy: got healthy result from https://192.168.55.8:2379 member 8b8904727bf526a5 is healthy: got healthy result from https://192.168.55.21:2379 member ed4f0efd277d7599 is healthy: got healthy result from https://192.168.55.13:2379 cluster is healthy
If you use the v3 etcd api, run the following command:
# ETCDCTL_API=3 etcdctl --cert="/etc/etcd/peer.crt" \ --key=/etc/etcd/peer.key \ --cacert="/etc/etcd/ca.crt" \ --endpoints="https://*master-0.example.com*:2379,\ https://*master-1.example.com*:2379,\ https://*master-2.example.com*:2379,\ https://*etcd0.example.com*:2379"\ endpoint health https://master-0.example.com:2379 is healthy: successfully committed proposal: took = 5.011358ms https://master-1.example.com:2379 is healthy: successfully committed proposal: took = 1.305173ms https://master-2.example.com:2379 is healthy: successfully committed proposal: took = 1.388772ms https://etcd0.example.com:2379 is healthy: successfully committed proposal: took = 1.498829ms
Modify each OpenShift Container Platform master
Modify the master configuration in the
etcClientInfo
section of the/etc/origin/master/master-config.yaml
file on every master. Add the new etcd host to the list of the etcd servers OpenShift Container Platform uses to store the data, and remove any failed etcd hosts:etcdClientInfo: ca: master.etcd-ca.crt certFile: master.etcd-client.crt keyFile: master.etcd-client.key urls: - https://master-0.example.com:2379 - https://master-1.example.com:2379 - https://master-2.example.com:2379 - https://etcd0.example.com:2379
Restart the master API service:
On every master:
# systemctl restart atomic-openshift-master-api
Or, on a single master cluster installation:
# systemctl restart atomic-openshift-master
WarningThe number of etcd nodes must be odd, so you must add at least two hosts.
If you use Flannel, modify the
flanneld
service configuration located at/etc/sysconfig/flanneld
on every OpenShift Container Platform host to include the new etcd host:FLANNEL_ETCD_ENDPOINTS=https://master-0.example.com:2379,https://master-1.example.com:2379,https://master-2.example.com:2379,https://etcd0.example.com:2379
Restart the
flanneld
service:# systemctl restart flanneld.service