etcd is the key value store for all object definitions, as well as the persistent master state. Other components watch for changes, then bring themselves into the desired state.

{product-title} versions prior to 3.5 used etcd version 2 (v2), while 3.5 and later use version 3 (v3). The data model between the two versions of etcd is different. etcd v3 can use both the v2 and v3 data model, whereas etcd v2 can only use the v2 data model. In an etcd v3 server, the v2 and v3 data stores exist in parallel and are independent.

For both v2 and v3 operations, you can use the ETCDCTL_API environment variable to use the proper API:

$ etcdctl -v
etcdctl version: 3.2.5
API version: 2
$ ETCDCTL_API=3 etcdctl version
etcdctl version: 3.2.5
API version: 3.2

See Migrating etcd Data (v2 to v3) section in the {product-title} 3.7 documentation for information about how to migrate to v3.

Back up and restore etcd

The etcd backup process is composed of two different procedures:

Configuration backup: Including the required etcd configuration and certificates
Data backup: Including both v2 and v3 data model.

The data backup procedure can be done on any host that has connectivity to the etcd cluster, where the proper certificates are provided, and where the etcdctl tool is installed.

Note	The backup files must be copied to an external system, ideally outside the {product-title} environment, and then encrypted.

etcd configuration backup

The etcd configuration files to be preserved are all stored in the /etc/etcd directory of the instances where etcd is running. This includes the etcd configuration file (/etc/etcd/etcd.conf) and the required certificates for cluster communication. All those files are generated at installation time by the Ansible installer.

To back up the etcd configuration:

$ ssh master-0
# mkdir -p /backup/etcd-config-$(date +%Y%m%d)/
# cp -R /etc/etcd/ /backup/etcd-config-$(date +%Y%m%d)/

Note	The backup is to be performed on every etcd member of the cluster as the certificates and configuration files are unique.

etcd configuration restore

The restore procedure for etcd configuration files replaces the appropriate files, then restarts the service.

If an etcd host has become corrupted and the /etc/etcd/etcd.conf file is lost, restore it using:

$ ssh master-0
# cp /backup/yesterday/master-0-files/etcd.conf /etc/etcd/etcd.conf
# restorecon -Rv /etc/etcd/etcd.conf
# systemctl restart etcd.service

In this example, the backup file is stored in the /backup/yesterday/master-0-files/etcd.conf path where it can be used as an external NFS share, S3 bucket, etc.

etcd data backup

Prerequisites

Note

The {product-title} installer creates aliases to avoid typing all the flags named etcdctl2 for etcd v2 tasks and etcdctl3 for etcd v3 tasks.

However, the etcdctl3 alias does not provide the full endpoint list to the etcdctl command, so the --endpoints option with all the endpoints must be provided.

Before backing up etcd:

etcdctl binaries should be available or, in containerized installations, the rhel7/etcd container should be available
Ensure connectivity with the etcd cluster (port 2379/tcp)

Ensure the proper certificates to connect to the etcd cluster

To ensure the etcd cluster is working, check its health:

# 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

Or if using the etcd v3 API:

# 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

Check the member list:

# etcdctl2 member list
2a371dd20f21ca8d: name=master-1.example.com peerURLs=https://192.168.55.12:2380 clientURLs=https://192.168.55.12:2379 isLeader=false
40bef1f6c79b3163: name=master-0.example.com peerURLs=https://192.168.55.8:2380 clientURLs=https://192.168.55.8:2379 isLeader=false
95dc17ffcce8ee29: name=master-2.example.com peerURLs=https://192.168.55.13:2380 clientURLs=https://192.168.55.13:2379 isLeader=true

Or, if using etcd the v3 API:

# etcdctl3 member list
2a371dd20f21ca8d, started, master-1.example.com, https://192.168.55.12:2380, https://192.168.55.12:2379
40bef1f6c79b3163, started, master-0.example.com, https://192.168.55.8:2380, https://192.168.55.8:2379
95dc17ffcce8ee29, started, master-2.example.com, https://192.168.55.13:2380, https://192.168.55.13:2379

Procedure

Note

While the etcdctl backup command is used to perform the backup, etcd v3 has no concept of a "backup". Instead, a "snapshot" may either be taken from a live member with the etcdctl snapshot save command or by copying the member/snap/db file from an etcd data directory.

The etcdctl backup command rewrites some of the metadata contained in the backup (specifically, the node ID and cluster ID), which means that in the backup, the node loses its former identity. In order to recreate a cluster from the backup, a new, single-node cluster is created, then the rest of the nodes join the cluster. The metadata is rewritten to prevent the new node from inadvertently being joined onto an existing cluster.

Perform the backup:
```
# mkdir -p */backup/etcd-$(date +%Y%m%d)*
# systemctl stop etcd.service
# etcdctl2 backup \
    --data-dir /var/lib/etcd \
    --backup-dir */backup/etcd-$(date +%Y%m%d)*
# cp /var/lib/etcd/member/snap/db */backup/etcd-$(date +%Y%m%d)*
# systemctl start etcd.service
```
While stopping the etcd service is not strictly necessary, doing so ensures that the etcd data is fully synchronized.

The etcdctl2 backup command creates etcd v2 data backup where copying the db file while the etcd service is not running is equivalent to running etcdctl3 snapshot for etcd v3 data backup:
```
# mkdir -p */backup/etcd-$(date +%Y%m%d)*
# etcdctl3 snapshot save */backup/etcd-$(date +%Y%m%d)*/db
Snapshot saved at /backup/etcd-<date>/db
# systemctl stop etcd.service
# etcdctl2 backup \
    --data-dir /var/lib/etcd \
    --backup-dir */backup/etcd-$(date +%Y%m%d)*
# systemctl start etcd.service
```
Note

The etcdctl snapshot save command requires the etcd service to be running.

In this example, a /backup/etcd-<date>/ directory is created, where <date> represents the current date, which must be an external NFS share, S3 bucket, or any external storage location.

In the case of an all-in-one cluster, the etcd data directory is located in /var/lib/origin/openshift.local.etcd

Restoring etcd v2 & v3 data

The following restores healthy data files and starts the etcd cluster as a single node, then adds the rest of the nodes in case an etcd cluster is required.

Procedure

Stop all etcd services:
```
# systemctl stop etcd.service
```
Clean the etcd data directories to ensure the proper backup is restored, but keeping the running copy:
```
# mv /var/lib/etcd /var/lib/etcd.old
# mkdir /var/lib/etcd
# chown -R etcd.etcd /var/lib/etcd/
# restorecon -Rv /var/lib/etcd/
```
Alternatively, you can wipe the etcd data directory:
```
# rm -Rf /var/lib/etcd/*
```
Note

In case an all-in-one cluster, the etcd data directory is located in /var/lib/origin/openshift.local.etcd
Restore a healthy backup data file to one of the etcd nodes:
```
# cp -R /backup/etcd-xxx/* /var/lib/etcd/
# mv /var/lib/etcd/db /var/lib/etcd/member/snap/db
```
Perform this step on all etcd hosts (including master hosts collocated with etcd).

Run the etcd service, forcing a new cluster.

This creates a custom file for the etcd service, which overwrites the execution command adding the --force-new-cluster option:

# mkdir -p /etc/systemd/system/etcd.service.d/
# echo "[Service]" > /etc/systemd/system/etcd.service.d/temp.conf
# echo "ExecStart=" >> /etc/systemd/system/etcd.service.d/temp.conf
# sed -n '/ExecStart/s/"$/ --force-new-cluster"/p' \
    /usr/lib/systemd/system/etcd.service \
    >> /etc/systemd/system/etcd.service.d/temp.conf

# systemctl daemon-reload
# systemctl restart etcd

Check for error messages:
```
$ journalctl -fu etcd.service
```

Check for health status (in this case, a single node):

# etcdctl2 cluster-health
member 5ee217d17301 is healthy: got healthy result from https://192.168.55.8:2379
cluster is healthy

Restart the etcd service in cluster mode:

# rm -f /etc/systemd/system/etcd.service.d/temp.conf
# systemctl daemon-reload
# systemctl restart etcd

Check for health status and member list

# etcdctl2 cluster-health
member 5ee217d17301 is healthy: got healthy result from https://192.168.55.8:2379
cluster is healthy

# etcdctl2 member list
5ee217d17301: name=master-0.example.com peerURLs=http://localhost:2380 clientURLs=https://192.168.55.8:2379 isLeader=true

Once the first instance is running, it is safe to restore multiple etcd servers as desired.

Fix the peerURLS parameter

After restoring the data and creating a new cluster, the peerURLs parameter shows localhost instead the IP where etcd is listening for peer communication:

# etcdctl2 member list
5ee217d17301: name=master-0.example.com peerURLs=http://*localhost*:2380 clientURLs=https://192.168.55.8:2379 isLeader=true

Procedure

Get the member ID from the etcdctl member list output.
Get the IP where etcd is listening for peer communication:
```
$ ss -l4n | grep 2380
```

Update the member information with that IP:

# etcdctl2 member update *5ee217d17301* https://*192.168.55.8*:2380
Updated member with ID 5ee217d17301 in cluster

To verify, check that the IP is in the output of the following:

$ etcdctl2 member list
5ee217d17301: name=master-0.example.com peerURLs=https://*192.168.55.8*:2380 clientURLs=https://192.168.55.8:2379 isLeader=true

Add more members

In the instance joining the cluster:

Get the etcd name for the instance in the ETCD_NAME variable:
```
# grep ETCD_NAME /etc/etcd/etcd.conf
```

Get the IP where etcd listens for peer communication:

# grep ETCD_INITIAL_ADVERTISE_PEER_URLS /etc/etcd/etcd.conf

Delete the previous etcd data:
```
# rm -Rf /var/lib/etcd/*
```
On the etcd host where etcd is properly running, add the new member:
```
$ etcdctl2 member add <name> <advertise_peer_urls>
```

The command outputs some variables. For example:

ETCD_NAME="master2"
ETCD_INITIAL_CLUSTER="master1=https://10.0.0.7:2380,master2=https://10.0.0.5:2380"
ETCD_INITIAL_CLUSTER_STATE="existing"

Add those values to the /etc/etcd/etcd.conf file of the new host:

# vi /etc/etc/etcd.conf

Once those values are replaced, start the etcd service in the node joining the cluster:
```
# systemctl start etcd.service
```
Check for error messages:
```
$ journalctl -fu etcd.service
```
Repeat the above for every etcd node joining the cluster.

Verify the cluster status and cluster health once all the nodes joined:

# etcdctl2 member list
5cd050b4d701: name=master1 peerURLs=https://10.0.0.7:2380 clientURLs=https://10.0.0.7:2379 isLeader=true
d0c57659d8990cbd: name=master2 peerURLs=https://10.0.0.5:2380 clientURLs=https://10.0.0.5:2379 isLeader=false
e4696d637de3eb2d: name=master3 peerURLs=https://10.0.0.6:2380 clientURLs=https://10.0.0.6:2379 isLeader=false

# etcdctl2 cluster-health
member 5cd050b4d701 is healthy: got healthy result from https://10.0.0.7:2379
member d0c57659d8990cbd is healthy: got healthy result from https://10.0.0.5:2379
member e4696d637de3eb2d is healthy: got healthy result from https://10.0.0.6:2379
cluster is healthy

Restoring etcd for v3

The restore procedure for v3 data is similar to the v2 data.

Snapshot integrity may be optionally verified at restore time. If the snapshot is taken with etcdctl snapshot save, it will have an integrity hash that is checked by etcdctl snapshot restore. If the snapshot is copied from the data directory, there is no integrity hash and it will only restore by using --skip-hash-check.

Important

The procedure to restore only the v3 data must be performed on a single etcd host. You can then add the rest of the nodes to the cluster.

Procedure

Stop all etcd services:
```
# systemctl stop etcd.service
```
Clear all old data, because etcdctl recreates it in the node where the restore procedure is going to be performed:
```
# rm -Rf /var/lib/etcd
```

Use the snapshot restore command with the data from /etc/etcd/etcd.conf to match the following command:

# etcdctl3 snapshot restore */backup/etcd-xxxxxx/backup.db* \
  --data-dir /var/lib/etcd \
  --name *master-0.example.com* \
  --initial-cluster *"master-0.example.com=https://192.168.55.8:2380"* \ --initial-cluster-token *"etcd-cluster-1"* \
  --initial-advertise-peer-urls *https://192.168.55.8:2380*

2017-10-03 08:55:32.440779 I | mvcc: restore compact to 1041269
2017-10-03 08:55:32.468244 I | etcdserver/membership: added member 40bef1f6c79b3163 [https://192.168.55.8:2380] to cluster 26841ebcf610583c

Restore permissions and selinux context to the restored files:

# chown -R etcd.etcd /var/lib/etcd/
# restorecon -Rv /var/lib/etcd

Start the etcd service:
```
# systemctl start etcd
```
Check for any error messages:
```
$ journalctl -fu etcd.service
```

Adding more nodes

Once the first instance is running, it is safe to restore multiple etcd servers as desired.

Procedure

Get the etcd name for the instance in the ETCD_NAME variable:
```
# grep ETCD_NAME /etc/etcd/etcd.conf
```

Get the IP where etcd listens for peer communication:

# grep ETCD_INITIAL_ADVERTISE_PEER_URLS /etc/etcd/etcd.conf

On the etcd host where etcd is still running, add the new member:

# etcdctl3 member add *<name>* \
  --peer-urls="*<advertise_peer_urls>*"

The command outputs some variables. For example:

ETCD_NAME="master2"
ETCD_INITIAL_CLUSTER="master-0.example.com=https://192.168.55.8:2380"
ETCD_INITIAL_CLUSTER_STATE="existing"

Add those values to the /etc/etcd/etcd.conf file of the new host:

# vi /etc/etc/etcd.conf

In the recently added etcd node, clean the etcd data directories to ensure the proper backup is restored keeping the running copy:
```
# mv /var/lib/etcd /var/lib/etcd.old
# mkdir /var/lib/etcd
# chown -R etcd.etcd /var/lib/etcd/
# restorecon -Rv /var/lib/etcd/
```
or wipe the etcd data directory:
```
# rm -Rf /var/lib/etcd/*
```
Start the etcd service in the recently added etcd host:
```
# systemctl start etcd
```
Check for errors:
```
# journalctl -fu etcd.service
```
Repeat the previous steps for every etcd node that is required to be added.

Verify the cluster has been properly set:

# etcdctl3 endpoint health
https://master-0.example.com:2379 is healthy: successfully committed proposal: took = 1.423459ms
https://master-1.example.com:2379 is healthy: successfully committed proposal: took = 1.767481ms
https://master-2.example.com:2379 is healthy: successfully committed proposal: took = 1.599694ms

# etcdctl3 endpoint status
https://master-0.example.com:2379, 40bef1f6c79b3163, 3.2.5, 28 MB, true, 9, 2878
https://master-1.example.com:2379, 1ea57201a3ff620a, 3.2.5, 28 MB, false, 9, 2878
https://master-2.example.com:2379, 59229711e4bc65c8, 3.2.5, 28 MB, false, 9, 2878

Scaling etcd

Scaling the etcd cluster can be performed vertically by adding more resources to the etcd hosts, or horizontally by adding more etcd hosts.

If etcd is collocated on master instances, horizontally scaling etcd prevents the API and controller services competing with etcd for resources.

Note	Due to the voting system etcd uses, the cluster must always contain an odd number of members.

The new host requires a fresh RHEL7 dedicated host. The etcd storage should be located on an SSD disk to achieve maximum performance and ideally on a dedicated disk mounted in /var/lib/etcd.

Note	{product-title} version 3.7 ships with an automated way to add a new etcd host using Ansible.

Prerequisites

Before adding 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:

# 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

Or, using etcd v3 API:

# 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.

Adding a new etcd host using Ansible

Procedure

Modify the Ansible inventory file and create a new group named [new_etcd] and add the new host. Then, add the new_etcd group as a child of the [OSEv3] group:

[OSEv3:children]
masters
nodes
etcd
<new_etcd>

... [OUTPUT ABBREVIATED] ...

[etcd]
master-0.example.com
master-1.example.com
master-2.example.com

[new_etcd]
etcd0.example.com

Run the etcd scaleup playbook from the host that executed the initial installation and where the Ansible inventory file is:
```
$ ansible-playbook  /usr/share/ansible/openshift-ansible/playbooks/byo/openshift-etcd/scaleup.yml
```

Once the above has finished, 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 using Flannel, modify the flanneld service configuration, located at /etc/sysconfig/flanneld on every {product-title} 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
```

Manually adding a new etcd host

The following steps can be performed on any etcd member. If using the Ansible installer, the first host provided in the [etcd] Ansible inventory is used to generate the etcd configuration and certificates stored in /etc/etcd/generated_certs, so perform the next steps in that etcd host.

Steps to be performed on the current etcd cluster

Procedure

In order to create the etcd certificates, run the openssl command with the proper values. To make this process easier, 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}"
export PREFIX="/etc/etcd/generated_certs/etcd-$CN/"
export OPENSSLCFG="/etc/etcd/ca/openssl.cnf"
```
Note

The custom openssl extensions used as etcd_v3_ca_* include the $SAN environment variable as subjectAltName. See /etc/etcd/ca/openssl.cnf for more information.
Create the directory where the configuration and certificates are stored:
```
# mkdir -p ${PREFIX}
```

Create the server certificate request and sign it:

# 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:

# 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 be modified later:
```
# cp /etc/etcd/etcd.conf ${PREFIX}
# cp /etc/etcd/ca.crt ${PREFIX}
```

Add the new host to the etcd cluster. Note the new host is not configured yet so the status stays as unstarted until the new host is properly configured:

# etcdctl2 member add ${NEW_ETCD_HOSTNAME} https://${NEW_ETCD_IP}:2380

This command outputs the following variables:

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"

Those values must be overwritten by the current ones in the sample ${PREFIX}/etcd.conf file. Also, modify the following variables with the new host IP (${NEW_ETCD_IP} can be used) in that file:
```
ETCD_LISTEN_PEER_URLS
ETCD_LISTEN_CLIENT_URLS
ETCD_INITIAL_ADVERTISE_PEER_URLS
ETCD_ADVERTISE_CLIENT_URLS
```
Modify the ${PREFIX}/etcd.conf file and check for syntax errors or missing IPs otherwise the etcd service could fail:
```
# vi ${PREFIX}/etcd.conf
```
Once the file has been properly modified, a tgz file with the certificates, the sample configuration file, and the ca is created and copied to the new host:
```
# tar -czvf /etc/etcd/generated_certs/${CN}.tgz -C ${PREFIX} .
# scp /etc/etcd/generated_certs/${CN}.tgz ${CN}:/tmp/
```

Steps to be performed on the new etcd host

The new host is required to be subscribed to the proper Red Hat software channels as explained above in the prerequisites section.

Procedure

Install iptables-services to provide iptables utilities to open the required ports for etcd:
```
# yum install -y iptables-services
```
Create 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
  Note
  
  In this example, a new chain OS_FIREWALL_ALLOW is created, which is the standard naming the {product-title} installer uses for firewall rules.
  
  Warning
  
  If 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 software:
```
# yum install -y etcd
```
Ensure the service is not running:
```
# systemctl disable etcd --now
```

Remove any etcd configuration and data:

# rm -Rf /etc/etcd/*
# rm -Rf /var/lib/etcd/*

Untar the certificates and configuration files

# tar xzvf /tmp/*etcd0.example.com*.tgz -C /etc/etcd/

Restore etcd configuration and data owner:

# chown -R etcd.etcd /etc/etcd/
# chown -R etcd.etcd /var/lib/etcd/

Start etcd on the new host:
```
# systemctl enable etcd --now
```

Verify the host has been added to the cluster and the current cluster health:

# 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

Or, using etcd v3 API:

# 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

Steps to be performed on all {product-title} masters

Procedure

Modify the master configuration to add the new etcd host to the list of the etcd servers {product-title} uses to store the data, located in the etcClientInfo section of the /etc/origin/master/master-config.yaml file on every master:

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

Warning

The number of etcd nodes must be odd, so at least two hosts must be added.

If using Flannel, the flanneld service configuration located at /etc/sysconfig/flanneld on every {product-title} host must be modified 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
```

Removing an etcd host

An etcd host can fail beyond restoration. This section walks through removing the failed etcd host from the cluster.

Important

Ensure the etcd cluster maintains quorum while removing the etcd host, by removing a single host at a time from a cluster.

Steps to be performed on all masters hosts

Procedure

Edit the failed etcd host out of the /etc/origin/master/master-config.yaml master configuration file on every master:

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* (1)

The host to be removed.

Restart the master API service on every master:
```
# systemctl restart atomic-openshift-master-api
```
Or, if using a single master cluster installation:
```
# systemctl restart atomic-openshift-master
```

Steps to be performed in the current etcd cluster

Procedure

Remove the failed host from the cluster by running the following on a functioning etcd host:

# etcdctl2 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
failed to check the health of member 8372784203e11288 on https://192.168.55.21:2379: Get https://192.168.55.21:2379/health: dial tcp 192.168.55.21:2379: getsockopt: connection refused
member 8372784203e11288 is unreachable: [https://192.168.55.21:2379] are all unreachable
member ed4f0efd277d7599 is healthy: got healthy result from https://192.168.55.13:2379
cluster is healthy

# etcdctl2 member remove 8372784203e11288
Removed member 8372784203e11288 from cluster

# etcdctl2 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

Note	The `remove` command requires the etcd ID, not the hostname.

To ensure the etcd configuration does not use the failed host when the etcd service is restarted, modify the /etc/etcd/etcd.conf file on all remaining etcd hosts and remove the failed host in the value for the ETCD_INITIAL_CLUSTER variable:
```
# vi /etc/etcd/etcd.conf
```
For example:
```
ETCD_INITIAL_CLUSTER=master-0.example.com=https://192.168.55.8:2380,master-1.example.com=https://192.168.55.12:2380,master-2.example.com=https://192.168.55.13:2380
```
becomes:
```
ETCD_INITIAL_CLUSTER=master-0.example.com=https://192.168.55.8:2380,master-1.example.com=https://192.168.55.12:2380
```
Note

Restarting the etcd services is not required, because the failed host has been removed using etcdctl on the command line.
Modify the Ansible inventory file to reflect the current status of the cluster and to avoid issues if running a playbook:
```
[OSEv3:children]
masters
nodes
etcd

... [OUTPUT ABBREVIATED] ...

[etcd]
master-0.example.com
master-1.example.com
```
If using Flannel, modify the flanneld service configuration located at /etc/sysconfig/flanneld on every host and remove the etcd host:
```
FLANNEL_ETCD_ENDPOINTS=https://master-0.example.com:2379,https://master-1.example.com:2379,https://master-2.example.com:2379
```
Restart the flanneld service:
```
# systemctl restart flanneld.service
```

Replacing an etcd host

To replace an etcd host, first remove the etcd node from the cluster following the steps from Removing an etcd host, then scale up the etcd cluster with the new host using the scale up Ansible playbook or the manual procedure in Scaling etcd.

Warning

The etcd cluster should maintain a quorum during the replacement operation. This means that at least one host should be in operation at all times.

If the host replacement operation occurs while the etcd cluster maintains a quorum, cluster operations are not affected, except if there is a large etcd data to replicate where some operations can be slowed down.

Note	Ensure a backup of etcd data and configuration files exists before any procedure involving the etcd cluster to ensure restoration in the case of failure.

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etcd_backup.adoc

etcd_backup.adoc

Back up and restore etcd

etcd configuration backup

etcd configuration restore

etcd data backup

Prerequisites

Procedure

Restoring etcd v2 & v3 data

Procedure

Procedure

Restoring etcd for v3

Procedure

Procedure

Scaling etcd

Prerequisites

Adding a new etcd host using Ansible

Procedure

Manually adding a new etcd host

Procedure

Procedure

Procedure

Removing an etcd host

Procedure

Procedure

Replacing an etcd host

Files

etcd_backup.adoc

Latest commit

History

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File metadata and controls

Back up and restore etcd

etcd configuration backup

etcd configuration restore

etcd data backup

Prerequisites

Procedure

Restoring etcd v2 & v3 data

Procedure

Procedure

Restoring etcd for v3

Procedure

Procedure

Scaling etcd

Prerequisites

Adding a new etcd host using Ansible

Procedure

Manually adding a new etcd host

Procedure

Procedure

Procedure

Removing an etcd host

Procedure

Procedure

Replacing an etcd host