Setup Highly Available ETCD Cluster on CentOS 7
The etcd is a strongly consistent, distributed key-value store that provides a reliable way to store data that needs to be accessed by a distributed system or cluster of machines. It gracefully handles leader elections during network partitions and can tolerate machine failure, even in the leader node.
1. Architecture Diagram#
2. System Requirements#
2.1. ETCD Nodes#
| Component | Description |
|---|---|
| Number of VMs | 3 |
| CPU | 2 Cores |
| Memory | 4 GB |
| Disk Size | 20 GB SSD |
| Operating System | CentOS 7 x64 |
| File System | XFS |
| Privileges | ROOT access prefered |
2.2. IP Allocation#
| Component | Description |
|---|---|
| VM IPs | 192.168.15.101 - 192.168.15.103 |
2.3. DNS Entries#
| IP | Hostname | FQDN |
|---|---|---|
| 192.168.15.101 | etcd-1 | etcd-1.example.com |
| 192.168.15.102 | etcd-2 | etcd-2.example.com |
| 192.168.15.103 | etcd-3 | etcd-3.example.com |
3. Install and Configure ETCD HA Cluster#
3.1. Install prerequisites on ALL nodes#
3.1.1. Set server hostname.
# Example:# sudo hostnamectl set-hostname etcd-1.example.com
sudo hostnamectl set-hostname <hostname>3.1.2. Install prerequisites.
# Clean YUM repository cachesudo yum clean all
# Update packagessudo yum update -y
# Install prerequisitessudo yum install -y vim curl ntp chrony net-tools yum-utils policycoreutils-python3.1.3. Synchronize server time with default NTP servers. If you have your own NTP servers, please make sure to update the /etc/chrony.conf
# Set timezone to Asia/Colombosudo timedatectl set-timezone Asia/Colombo
# Enable NTP time synchronizationsudo timedatectl set-ntp true3.1.4. Start and enable chronyd service.
# Start and enable chronyd servicesudo systemctl enable --now chronyd
# Verify if the service is startedsudo systemctl status chronyd3.1.5. Display time synchronization status.
# Verify synchronisation statesudo ntpstat
# Check Chrony Source Statisticssudo chronyc sourcestats -v3.1.6. Disable File Access Time Logging and enable Combat Fragmentation to enhance XFS file system performance. Add noatime,nodiratime,allocsize=64m to all XFS volumes under /etc/fstab.
# Edit /etc/fstabsudo vim /etc/fstab
# Modify XFS volume entries as follows# Example:UUID="03c97344-9b3d-45e2-9140-cbbd57b6f085" / xfs defaults,noatime,nodiratime,allocsize=64m 0 03.1.7. Tweaking the system for high concurrency and security.
cat <<"EOF" | sudo tee /etc/sysctl.d/00-sysctl.conf > /dev/null############################################################################################## Tweak virtual memory#############################################################################################
# Default: 30# 0 - Never swap under any circumstances.# 1 - Do not swap unless there is an out-of-memory (OOM) condition.vm.swappiness = 30
# vm.dirty_background_ratio is used to adjust how the kernel handles dirty pages that must be flushed to disk.# Default value is 10.# The value is a percentage of the total amount of system memory, and setting this value to 5 is appropriate in many situations.# This setting should not be set to zero.vm.dirty_background_ratio = 5
# The total number of dirty pages that are allowed before the kernel forces synchronous operations to flush them to disk# can also be increased by changing the value of vm.dirty_ratio, increasing it to above the default of 30 (also a percentage of total system memory)# vm.dirty_ratio value in-between 60 and 80 is a reasonable number.vm.dirty_ratio = 60
# vm.max_map_count will calculate the current number of memory-mapped files.# The minimum value for mmap limit (vm.max_map_count) is the number of open files ulimit (cat /proc/sys/fs/file-max).# map_count should be around 1 per 128 KB of system memory. Therefore, max_map_count will be 262144 on a 32 GB system.# Reference: https://docs.confluent.io/current/kafka/deployment.html# Default: 65530vm.max_map_count = 2097152
############################################################################################## Tweak file descriptors#############################################################################################
# Increases the size of file descriptors and inode cache and restricts core dumps.fs.file-max = 2097152fs.suid_dumpable = 0
############################################################################################## Tweak network settings#############################################################################################
# Default amount of memory allocated for the send and receive buffers for each socket.# This will significantly increase performance for large transfers.net.core.wmem_default = 25165824net.core.rmem_default = 25165824
# Maximum amount of memory allocated for the send and receive buffers for each socket.# This will significantly increase performance for large transfers.net.core.wmem_max = 25165824net.core.rmem_max = 25165824
# In addition to the socket settings, the send and receive buffer sizes for# TCP sockets must be set separately using the net.ipv4.tcp_wmem and net.ipv4.tcp_rmem parameters.# These are set using three space-separated integers that specify the minimum, default, and maximum sizes, respectively.# The maximum size cannot be larger than the values specified for all sockets using net.core.wmem_max and net.core.rmem_max.# A reasonable setting is a 4 KiB minimum, 64 KiB default, and 2 MiB maximum buffer.net.ipv4.tcp_wmem = 20480 12582912 25165824net.ipv4.tcp_rmem = 20480 12582912 25165824
# Increase the maximum total buffer-space allocatable# This is measured in units of pages (4096 bytes)net.ipv4.tcp_mem = 65536 25165824 262144net.ipv4.udp_mem = 65536 25165824 262144
# Minimum amount of memory allocated for the send and receive buffers for each socket.net.ipv4.udp_wmem_min = 16384net.ipv4.udp_rmem_min = 16384
# Enabling TCP window scaling by setting net.ipv4.tcp_window_scaling to 1 will allow# clients to transfer data more efficiently, and allow that data to be buffered on the broker side.net.ipv4.tcp_window_scaling = 1
# Increasing the value of net.ipv4.tcp_max_syn_backlog above the default of 1024 will allow# a greater number of simultaneous connections to be accepted.net.ipv4.tcp_max_syn_backlog = 10240
# Increasing the value of net.core.netdev_max_backlog to greater than the default of 1000# can assist with bursts of network traffic, specifically when using multigigabit network connection speeds,# by allowing more packets to be queued for the kernel to process them.net.core.netdev_max_backlog = 65536
# Increase the maximum amount of option memory buffersnet.core.optmem_max = 25165824
# Number of times SYNACKs for passive TCP connection.net.ipv4.tcp_synack_retries = 2
# Allowed local port range.net.ipv4.ip_local_port_range = 2048 65535
# Protect Against TCP Time-Wait# Default: net.ipv4.tcp_rfc1337 = 0net.ipv4.tcp_rfc1337 = 1
# Decrease the time default value for tcp_fin_timeout connectionnet.ipv4.tcp_fin_timeout = 15
# The maximum number of backlogged sockets.# Default is 128.net.core.somaxconn = 4096
# Turn on syncookies for SYN flood attack protection.net.ipv4.tcp_syncookies = 1
# Avoid a smurf attacknet.ipv4.icmp_echo_ignore_broadcasts = 1
# Turn on protection for bad icmp error messagesnet.ipv4.icmp_ignore_bogus_error_responses = 1
# Enable automatic window scaling.# This will allow the TCP buffer to grow beyond its usual maximum of 64K if the latency justifies it.net.ipv4.tcp_window_scaling = 1
# Turn on and log spoofed, source routed, and redirect packetsnet.ipv4.conf.all.log_martians = 1net.ipv4.conf.default.log_martians = 1
# Tells the kernel how many TCP sockets that are not attached to any# user file handle to maintain. In case this number is exceeded,# orphaned connections are immediately reset and a warning is printed.# Default: net.ipv4.tcp_max_orphans = 65536net.ipv4.tcp_max_orphans = 65536
# Do not cache metrics on closing connectionsnet.ipv4.tcp_no_metrics_save = 1
# Enable timestamps as defined in RFC1323:# Default: net.ipv4.tcp_timestamps = 1net.ipv4.tcp_timestamps = 1
# Enable select acknowledgments.# Default: net.ipv4.tcp_sack = 1net.ipv4.tcp_sack = 1
# Increase the tcp-time-wait buckets pool size to prevent simple DOS attacks.# net.ipv4.tcp_tw_recycle has been removed from Linux 4.12. Use net.ipv4.tcp_tw_reuse instead.net.ipv4.tcp_max_tw_buckets = 1440000net.ipv4.tcp_tw_reuse = 1
# The accept_source_route option causes network interfaces to accept packets with the Strict Source Route (SSR) or Loose Source Routing (LSR) option set. # The following setting will drop packets with the SSR or LSR option set.net.ipv4.conf.all.accept_source_route = 0net.ipv4.conf.default.accept_source_route = 0
# Turn on reverse path filteringnet.ipv4.conf.all.rp_filter = 1net.ipv4.conf.default.rp_filter = 1
# Disable ICMP redirect acceptancenet.ipv4.conf.all.accept_redirects = 0net.ipv4.conf.default.accept_redirects = 0net.ipv4.conf.all.secure_redirects = 0net.ipv4.conf.default.secure_redirects = 0
# Disables sending of all IPv4 ICMP redirected packets.net.ipv4.conf.all.send_redirects = 0net.ipv4.conf.default.send_redirects = 0
# Disable IP forwarding.# IP forwarding is the ability for an operating system to accept incoming network packets on one interface, # recognize that it is not meant for the system itself, but that it should be passed on to another network, and then forwards it accordingly.net.ipv4.ip_forward = 0
# Disable IPv6net.ipv6.conf.all.disable_ipv6 = 1net.ipv6.conf.default.disable_ipv6 = 1
############################################################################################## Tweak kernel parameters#############################################################################################
# Address Space Layout Randomization (ASLR) is a memory-protection process for operating systems that guards against buffer-overflow attacks.# It helps to ensure that the memory addresses associated with running processes on systems are not predictable,# thus flaws or vulnerabilities associated with these processes will be more difficult to exploit.# Accepted values: 0 = Disabled, 1 = Conservative Randomization, 2 = Full Randomizationkernel.randomize_va_space = 2
# Allow for more PIDs (to reduce rollover problems)kernel.pid_max = 65536EOF3.1.8. Reload all sysctl variables without rebooting the server.
sudo sysctl -p /etc/sysctl.d/00-sysctl.conf3.1.9. Create Local DNS records.
cat <<"EOF" | sudo tee /etc/hosts > /dev/null# localhost127.0.0.1 localhost localhost.localdomain
# When DNS records are updated in the DNS server, remove these entries.192.168.15.101 etcd-1 etcd-1.example.com192.168.15.102 etcd-2 etcd-2.example.com192.168.15.103 etcd-3 etcd-3.example.comEOF3.1.10. The servers need to be restarted before continuing further.
sudo reboot3.2. ETCD common configurations on ALL nodes#
3.2.1. Download and install the latest ETCD binary from GitHub.
important
You can download the latest ETCD binary from here.
# Set ETCD versionETCD_VER=v3.4.14
# Download the latest tarballcurl -L -o /tmp/etcd-${ETCD_VER}-linux-amd64.tar.gz https://storage.googleapis.com/etcd/${ETCD_VER}/etcd-${ETCD_VER}-linux-amd64.tar.gz
# Extract the downloaded tarballtar xfz /tmp/etcd-${ETCD_VER}-linux-amd64.tar.gz -C /tmp
# Move extracted binaries to /usr/local/binsudo mv /tmp/etcd-${ETCD_VER}-linux-amd64/etcd /usr/local/binsudo mv /tmp/etcd-${ETCD_VER}-linux-amd64/etcdctl /usr/local/bin
# Set permissionssudo chown root:root /usr/local/bin/etcdsudo chown root:root /usr/local/bin/etcdctl
# Remove temporary filessudo rm -rf /tmp/etcd-${ETCD_VER}-linux-amd64*3.2.2. Create ETCD service user.
# Create ETCD service usersudo useradd --system --no-create-home etcd3.2.3. Create ETCD directory structure and provide necessary permissions.
# Create ETCD directory structuresudo mkdir -p /etc/etcd/tls /var/lib/etcd
# Provide necessary permissionssudo chown -R etcd:etcd /etc/etcd /var/lib/etcdsudo chmod 0700 /var/lib/etcd
# Restore SELinux contextsudo restorecon -RvF /etc/etcd /var/lib/etcd3.2.4. Copy the correct SSL certificate, SSL key and the CA certificate files under /etc/etcd/tls
important
- To generate a custom CA and CA signed SSL certificates, please follow this guide.
- Other than the *.example.com domain, you must have 'localhost' as a Subject Alternative Name (SAN) since etcdctl uses it for internal API calls.
# Copy the correct CA certificate, TLS certificate and TLS key/etc/etcd/tls/ca.pem/etc/etcd/tls/tls.crt/etc/etcd/tls/tls.key
# Set correct permissionssudo chown -R etcd:etcd /etc/etcd/tlssudo chmod 0600 /etc/etcd/tls/*
# Restore SELinux contextsudo restorecon -RvF /etc/etcd/tls
# If you are using a self-signed certificate, make sure to configure it as a trusted root certificatesudo cp /etc/etcd/tls/ca.pem /etc/pki/ca-trust/source/anchors/ca.pemsudo update-ca-trust3.2.5. Open necessary firewall ports.
sudo firewall-cmd --permanent --add-port={2379,2380}/tcpsudo firewall-cmd --reload3.2.6. Create ETCD Systemd service.
# Create ETCD Systemd servicecat <<EOF | sudo tee /etc/systemd/system/etcd.service > /dev/null[Unit]Description="ETCD Service"Documentation=https://github.com/etcd-io/etcdAfter=network.target [Service]Type=notifyUser=etcdGroup=etcdProtectSystem=fullProtectHome=read-onlyPrivateTmp=yesPrivateDevices=yesSecureBits=keep-capsAmbientCapabilities=CAP_IPC_LOCKNoNewPrivileges=yesEnvironmentFile=/etc/etcd/etcd.confExecStart=/usr/local/bin/etcdRestart=alwaysRestartSec=10sLimitNOFILE=40000 [Install]WantedBy=multi-user.targetEOF3.2.7. Restore SELinux context.
# Restore SELinux contextsudo restorecon -Fv /etc/systemd/system/etcd.service3.2.8. Reload systemd manager configurations.
# Reload systemd manager configurationssudo systemctl daemon-reload3.3. Configurations on ETCD-1 node.#
3.3.1. Add the configurations under /etc/etcd/etcd.conf
# ETCD-1 configurationscat <<"EOF" | sudo tee /etc/etcd/etcd.conf > /dev/nullETCD_NAME=ETCD-1ETCD_DATA_DIR="/var/lib/etcd"ETCD_LISTEN_PEER_URLS="https://0.0.0.0:2380"ETCD_LISTEN_CLIENT_URLS="https://0.0.0.0:2379"ETCD_INITIAL_CLUSTER_TOKEN="etcd-cluster"ETCD_INITIAL_CLUSTER="ETCD-1=https://etcd-1.example.com:2380,ETCD-2=https://etcd-2.example.com:2380,ETCD-3=https://etcd-3.example.com:2380"ETCD_INITIAL_ADVERTISE_PEER_URLS="https://etcd-1.example.com:2380"ETCD_ADVERTISE_CLIENT_URLS="https://etcd-1.example.com:2379"ETCD_TRUSTED_CA_FILE="/etc/etcd/tls/ca.pem"ETCD_CERT_FILE="/etc/etcd/tls/tls.crt"ETCD_KEY_FILE="/etc/etcd/tls/tls.key"ETCD_PEER_CLIENT_CERT_AUTH=trueETCD_PEER_TRUSTED_CA_FILE="/etc/etcd/tls/ca.pem"ETCD_PEER_KEY_FILE="/etc/etcd/tls/tls.key"ETCD_PEER_CERT_FILE="/etc/etcd/tls/tls.crt"EOF3.3.2. Set correct permissions.
# Set permissionssudo chown etcd:etcd /etc/etcd/etcd.confsudo chmod 0644 /etc/etcd/etcd.conf
# Restore SELinux contextsudo restorecon -RvF /etc/etcd3.3.3. Start and enable etcd.service.
# Start and enable etcd.servicesudo systemctl enable --now etcd.service3.3.4. If there are any errors, please check systemd logs.
# Check error messages in journaldsudo journalctl -f -b --no-pager -u etcd3.4. Configurations on ETCD-2 node.#
3.4.1. Add the configurations under /etc/etcd/etcd.conf
# ETCD-2 configurationscat <<"EOF" | sudo tee /etc/etcd/etcd.conf > /dev/nullETCD_NAME=ETCD-2ETCD_DATA_DIR="/var/lib/etcd"ETCD_LISTEN_PEER_URLS="https://0.0.0.0:2380"ETCD_LISTEN_CLIENT_URLS="https://0.0.0.0:2379"ETCD_INITIAL_CLUSTER_TOKEN="etcd-cluster"ETCD_INITIAL_CLUSTER="ETCD-1=https://etcd-1.example.com:2380,ETCD-2=https://etcd-2.example.com:2380,ETCD-3=https://etcd-3.example.com:2380"ETCD_INITIAL_ADVERTISE_PEER_URLS="https://etcd-2.example.com:2380"ETCD_ADVERTISE_CLIENT_URLS="https://etcd-2.example.com:2379"ETCD_TRUSTED_CA_FILE="/etc/etcd/tls/ca.pem"ETCD_CERT_FILE="/etc/etcd/tls/tls.crt"ETCD_KEY_FILE="/etc/etcd/tls/tls.key"ETCD_PEER_CLIENT_CERT_AUTH=trueETCD_PEER_TRUSTED_CA_FILE="/etc/etcd/tls/ca.pem"ETCD_PEER_KEY_FILE="/etc/etcd/tls/tls.key"ETCD_PEER_CERT_FILE="/etc/etcd/tls/tls.crt"EOF3.4.2. Set correct permissions.
# Set permissionssudo chown etcd:etcd /etc/etcd/etcd.confsudo chmod 0644 /etc/etcd/etcd.conf
# Restore SELinux contextsudo restorecon -RvF /etc/etcd3.4.3. Start and enable etcd.service.
# Start and enable etcd.servicesudo systemctl enable --now etcd.service3.4.4. If there are any errors, please check systemd logs.
# Check error messages in journaldsudo journalctl -f -b --no-pager -u etcd3.5. Configurations on ETCD-3 node.#
3.5.1. Add the configurations under /etc/etcd/etcd.conf
# ETCD-3 configurationscat <<"EOF" | sudo tee /etc/etcd/etcd.conf > /dev/nullETCD_NAME=ETCD-3ETCD_DATA_DIR="/var/lib/etcd"ETCD_LISTEN_PEER_URLS="https://0.0.0.0:2380"ETCD_LISTEN_CLIENT_URLS="https://0.0.0.0:2379"ETCD_INITIAL_CLUSTER_TOKEN="etcd-cluster"ETCD_INITIAL_CLUSTER="ETCD-1=https://etcd-1.example.com:2380,ETCD-2=https://etcd-2.example.com:2380,ETCD-3=https://etcd-3.example.com:2380"ETCD_INITIAL_ADVERTISE_PEER_URLS="https://etcd-3.example.com:2380"ETCD_ADVERTISE_CLIENT_URLS="https://etcd-3.example.com:2379"ETCD_TRUSTED_CA_FILE="/etc/etcd/tls/ca.pem"ETCD_CERT_FILE="/etc/etcd/tls/tls.crt"ETCD_KEY_FILE="/etc/etcd/tls/tls.key"ETCD_PEER_CLIENT_CERT_AUTH=trueETCD_PEER_TRUSTED_CA_FILE="/etc/etcd/tls/ca.pem"ETCD_PEER_KEY_FILE="/etc/etcd/tls/tls.key"ETCD_PEER_CERT_FILE="/etc/etcd/tls/tls.crt"EOF3.5.2. Set correct permissions.
# Set permissionssudo chown etcd:etcd /etc/etcd/etcd.confsudo chmod 0644 /etc/etcd/etcd.conf
# Restore SELinux contextsudo restorecon -RvF /etc/etcd3.5.3. Start and enable etcd.service.
# Start and enable etcd.servicesudo systemctl enable --now etcd.service3.5.4. If there are any errors, please check systemd logs.
# Check error messages in journaldsudo journalctl -f -b --no-pager -u etcd4. Maintenance#
4.1. Verify ETCD Cluster Health#
4.1.1. Checks the healthiness of endpoints.
# Checks the healthiness of endpointsETCDCTL_API=3 etcdctl endpoint health \ --endpoints="https://localhost:2379" \ --cacert /etc/etcd/tls/ca.pem \ --cert /etc/etcd/tls/tls.crt \ --key /etc/etcd/tls/tls.key \ --debug4.1.2. Prints out the status of endpoints.
# Prints out the status of endpointsETCDCTL_API=3 etcdctl endpoint status \ --endpoints="https://localhost:2379" \ --cacert /etc/etcd/tls/ca.pem \ --cert /etc/etcd/tls/tls.crt \ --key /etc/etcd/tls/tls.key \ --debug4.2. Backup and Restore an ETCD Cluster#
4.2.1. Create an ETCD snapshot.
important
Recovering a cluster first needs a snapshot of the keyspace from an etcd member.
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.
For example, the following command snapshots the keyspace to the file snapshot.db
# Create a ETCD snapshotETCDCTL_API=3 etcdctl snapshot save snapshot.db \ --endpoints="https://localhost:2379" \ --cacert /etc/etcd/tls/ca.pem \ --cert /etc/etcd/tls/tls.crt \ --key /etc/etcd/tls/tls.key \ --debug4.2.2. Restore an ETCD Cluster.
important
To restore a cluster, all that is needed is a single snapshot db file. A cluster restore with etcdctl snapshot restore creates new etcd data directories; all members should restore using the same snapshot. Restoring overwrites some snapshot metadata (specifically, the member ID and cluster ID); the member loses its former identity. This metadata overwrite prevents the new member from inadvertently joining an existing cluster. Therefore in order to start a cluster from a snapshot, the restore must start a new logical cluster.
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 the configuration flag
--skip-hash-check=true.A restore initializes a new member of a new cluster, with a fresh cluster configuration using etcd's cluster configuration flags, but preserves the contents of the etcd keyspace. Continuing from the previous example, the following creates new etcd data directories under /var/lib/etcd for a three member cluster.
Before you execute the following commands, please make sure to BACKUP /var/lib/etcd directory.
4.2.2.1. Stop ETCD service and remove /var/lib/etcd directory on ALL nodes.
# Stop ETCD servicesudo systemctl stop etcd
# Remove /var/lib/etcd directorysudo rm -rf /var/lib/etcd4.2.2.2. Restore ETCD-1 node.
# Restore ETCD-1ETCDCTL_API=3 etcdctl snapshot restore snapshot.db \ --name ETCD-1 \ --data-dir /var/lib/etcd \ --initial-cluster-token "etcd-cluster" \ --initial-advertise-peer-urls https://etcd-1.example.com:2380 \ --initial-cluster "ETCD-1=https://etcd-1.example.com:2380,ETCD-2=https://etcd-2.example.com:2380,ETCD-3=https://etcd-3.example.com:2380"4.2.2.3. Restore ETCD-2 node.
# Restore ETCD-2ETCDCTL_API=3 etcdctl snapshot restore snapshot.db \ --name ETCD-2 \ --data-dir /var/lib/etcd \ --initial-cluster-token "etcd-cluster" \ --initial-advertise-peer-urls https://etcd-2.example.com:2380 \ --initial-cluster "ETCD-1=https://etcd-1.example.com:2380,ETCD-2=https://etcd-2.example.com:2380,ETCD-3=https://etcd-3.example.com:2380"4.2.2.4. Restore ETCD-3 node.
# Restore ETCD-3ETCDCTL_API=3 etcdctl snapshot restore snapshot.db \ --name ETCD-3 \ --data-dir /var/lib/etcd \ --initial-cluster-token "etcd-cluster" \ --initial-advertise-peer-urls https://etcd-3.example.com:2380 \ --initial-cluster "ETCD-1=https://etcd-1.example.com:2380,ETCD-2=https://etcd-2.example.com:2380,ETCD-3=https://etcd-3.example.com:2380"4.2.2.5. Set necessary permissions and SELinux context on ALL nodes.
# Set necessary permissionssudo chown -R etcd:etcd /var/lib/etcdsudo chmod 0700 /var/lib/etcd
# Restore SELinux contextsudo restorecon -RvF /var/lib/etcd4.2.2.6. Start ETCD service on ALL nodes.
# Start ETCD servicesudo systemctl start etcd
# Verify if the ETCD service is runningsudo systemctl status etcd4.2.2.7. If there are any errors, please check systemd logs.
# Check error messages in journaldsudo journalctl -f -b --no-pager -u etcd