ZDT Replicate: Complete Configuration Guide

Welcome to our comprehensive guide on configuring ZDT Replicate, a powerful tool that simplifies DRBD (Distributed Replicated Block Device) management for Zero Downtime deployments. Whether you’re setting up high availability within a single datacenter or implementing disaster recovery across multiple sites, this guide will help you understand all available configuration options.

Configuration File Basics

ZDT Replicate uses a simple environment file (zdtreplicate.env) to store all configuration parameters.

This file must be located in your ZDT DevOps installation config directory:

The file uses a simple KEY=VALUE format, with parameters organized into logical sections. If the file doesn’t exist, you’ll need to create it in the correct location before running zdtreplicate commands.

Important: Make sure you have appropriate permissions to write to the config directory. In most installations, this requires sudo or administrator privileges.

Node Configuration

ZDTREP_NODE_TYPE

This parameter defines the role of the node in your replication topology.

Possible values	`primary`, `secondary`, `mirror`, `external`
Default	`primary`
Description	`primary`: Active node that serves data (read/write access) `secondary`: Standby node in local cluster for quick failover `mirror`: Node that replicates data to external datacenter `external`: Node in separate datacenter receiving replication
Example	`ZDTREP_NODE_TYPE=primary`

ZDTREP_NODE_ID

A unique identifier for this node in the DRBD configuration.

Default	None (required)
Description	Should be a simple string without spaces
Example	`ZDTREP_NODE_ID=nodeA`

ZDTREP_CLUSTER_ADDR

IP address or hostname of this node.

Default	`127.0.0.1`
Description	Used for DRBD network communication
Example	`ZDTREP_CLUSTER_ADDR=192.168.1.1`

ZDTREP_DISK_DEVICE

Block device to be used for DRBD replication.

Default	`/dev/sdb1`
Description	The device will store replicated data. Warning: All data on this device will be erased during setup.
Example	`ZDTREP_DISK_DEVICE=/dev/sdb1`

ZDTREP_DATA_DIR

Directory where the DRBD device will be mounted.

Default	`/var/lib/etcd`
Description	Typically where your application (e.g., etcd) will store its data
Example	`ZDTREP_DATA_DIR=/var/lib/etcd`

Replication Configuration

ZDTREP_REPLICATION_PROTOCOL

DRBD replication protocol determining data consistency vs. performance trade-offs.

Possible values	`A`, `B`, `C`
Default	`C`
Description	`A`: Asynchronous replication (fastest, potential data loss) `B`: Semi-synchronous (confirms network receipt, not disk write) `C`: Synchronous (slowest but safest, no data loss)
Recommendation	Use `C` for local nodes, `A` for cross-datacenter replication
Example	`ZDTREP_REPLICATION_PROTOCOL=C`

ZDTREP_REPLICATION_PORT

Base TCP port for DRBD replication.

Default	`7788`
Description	DRBD will use this port for network communication. Make sure this port is open in your firewall.
Example	`ZDTREP_REPLICATION_PORT=7788`

ZDTREP_BANDWIDTH_LIMIT

Network bandwidth limit for replication.

Default	`0` (unlimited)
Format	Number followed by K, M, or G (e.g., 10M for 10 megabits/sec)
Description	Especially useful for cross-datacenter replication to avoid network saturation
Example	`ZDTREP_BANDWIDTH_LIMIT=10M`

Remote Node Addresses

ZDTREP_PRIMARY_ADDR

IP address of the primary node.

Default	Empty
Required for	Secondary and mirror nodes
Example	`ZDTREP_PRIMARY_ADDR=192.168.1.1`

ZDTREP_SECONDARY_ADDR

IP address of the secondary node.

Default	Empty
Required for	Mirror nodes
Example	`ZDTREP_SECONDARY_ADDR=192.168.1.2`

ZDTREP_MIRROR_ADDRS

Comma-separated list of mirror node addresses.

Default	Empty
Required for	External nodes
Example	`ZDTREP_MIRROR_ADDRS=10.0.0.1,10.0.0.2,10.0.0.3`

Monitoring Configuration

ZDTREP_MONITOR_INTERVAL

Time between status checks in seconds.

Default	`60`
Description	Controls how frequently the monitor command checks replication status
Example	`ZDTREP_MONITOR_INTERVAL=60`

ZDTREP_MONITOR_LOG_PATH

Full path to monitoring log file.

Default	`/var/log/zdtreplicate.log`
Description	The monitor command will write status information to this file
Example	`ZDTREP_MONITOR_LOG_PATH=/var/log/zdtreplicate.log`

NFS Configuration (Optional)

ZDTREP_NFS_ENABLED

Enable NFS exports of the DRBD device.

Possible values	`true`, `false`
Default	`false`
Description	Automatically configure NFS sharing of the replicated data. Useful for Kubernetes PVC integration.
Example	`ZDTREP_NFS_ENABLED=true`

ZDTREP_NFS_EXPORTS_DIR

Directory to export via NFS.

Default	`/mnt/etcd-data`
Description	Typically the same as ZDTREP_DATA_DIR or a subdirectory
Example	`ZDTREP_NFS_EXPORTS_DIR=/mnt/etcd-data`

ZDTREP_NFS_ALLOWED_CLIENTS

Clients allowed to access the NFS export.

Default	`*` (all clients)
Format	NFS exports syntax (* for all, IP/subnet for specific clients)
Example	`ZDTREP_NFS_ALLOWED_CLIENTS=192.168.0.0/24`

ZDTREP_NFS_OPTIONS

NFS export options.

Default	`rw,sync,no_subtree_check`
Common options	`rw`: Allow read/write access `sync`: Synchronous writes (safer) `no_subtree_check`: Disable subtree checking (better performance) `no_root_squash`: Allow root access (use with caution)
Example	`ZDTREP_NFS_OPTIONS=rw,sync,no_subtree_check`

Advanced Options

ZDTREP_METADATA_OPTIONS

Additional options for DRBD metadata creation.

Default	Empty
Description	These options are passed directly to the ‘drbdadm create-md’ command
Example	`ZDTREP_METADATA_OPTIONS=--max-peers=32`

ZDTREP_RESOURCE_NAME_PREFIX

Prefix for DRBD resource names.

Default	`etcd-data`
Description	The full resource name will be this prefix followed by the node ID
Example	`ZDTREP_RESOURCE_NAME_PREFIX=etcd-data`

Creating and Editing the Configuration File

The zdtreplicate.env configuration file is available for download from the ZDT DevOps community repository on GitHub:

👉 Download zdtreplicate.env

After downloading, place it in your configuration directory:

<your ZDT DevOps Installation path>/DevOps/config/zdtreplicate.env

Then, set the appropriate permissions:

sudo chmod 644 <your ZDT DevOps Installation path>/DevOps/config/zdtreplicate.env

You can still use your preferred text editor (e.g., nano, vim, code) to review or customize the configuration file as needed.

Configuration Examples

Primary Node in Main Datacenter

ZDTREP_NODE_TYPE=primary
ZDTREP_NODE_ID=nodeA
ZDTREP_CLUSTER_ADDR=192.168.1.1
ZDTREP_DISK_DEVICE=/dev/sdb1
ZDTREP_DATA_DIR=/var/lib/etcd
ZDTREP_REPLICATION_PROTOCOL=C
ZDTREP_REPLICATION_PORT=7788
ZDTREP_NFS_ENABLED=true
ZDTREP_NFS_EXPORTS_DIR=/mnt/etcd-data

Secondary Node in Main Datacenter

ZDTREP_NODE_TYPE=secondary
ZDTREP_NODE_ID=nodeB
ZDTREP_CLUSTER_ADDR=192.168.1.2
ZDTREP_DISK_DEVICE=/dev/sdb1
ZDTREP_DATA_DIR=/var/lib/etcd
ZDTREP_PRIMARY_ADDR=192.168.1.1
ZDTREP_REPLICATION_PROTOCOL=C
ZDTREP_REPLICATION_PORT=7788

Mirror Node in External Datacenter

ZDTREP_NODE_TYPE=mirror
ZDTREP_NODE_ID=dcmirror
ZDTREP_CLUSTER_ADDR=10.0.0.1
ZDTREP_DISK_DEVICE=/dev/sdb1
ZDTREP_DATA_DIR=/var/lib/etcd
ZDTREP_PRIMARY_ADDR=192.168.1.1
ZDTREP_SECONDARY_ADDR=192.168.1.2
ZDTREP_REPLICATION_PROTOCOL=A
ZDTREP_REPLICATION_PORT=7788
ZDTREP_BANDWIDTH_LIMIT=10M

Troubleshooting

If you encounter issues with your configuration:

Verify that the configuration file exists in the correct location (<your ZDT DevOps Installation path>/DevOps/config/zdtreplicate.env)
Check that the file has the correct permissions (readable by the ZDT system)
Check the log file specified in ZDTREP_MONITOR_LOG_PATH
Verify that the disk device specified in ZDTREP_DISK_DEVICE exists and is not in use
Ensure network connectivity between nodes on the port specified in ZDTREP_REPLICATION_PORT
Check firewall rules to allow DRBD traffic between nodes

Conclusion

The ZDT Replicate configuration system is designed to be flexible yet straightforward, allowing you to set up complex replication topologies with minimal effort. By properly configuring the parameters described in this guide and placing the configuration file in the correct ZDT DevOps config directory, you can create a robust Zero Downtime infrastructure that protects your data against both hardware failures and datacenter outages.

If you have questions or need assistance with your ZDT Replicate configuration, please reach out to our support team.

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