Redis Master-Replica Setup on Ubuntu 24.04

Redis is an in-memory data store used as a database, cache, and message broker. In this guide, we will set up a master-replica replication between two Ubuntu 24.04 servers for high availability and read scaling.

Redis now generally uses the term primary/replica. “Master/slave” is still commonly seen in configuration and documentation.

Server Details

Role	Hostname	IP
Master	redis-master	192.168.1.101
Replica	redis-slave	192.168.1.102

---

1. Configure Hostnames

Master — 192.168.1.101:

sudo hostnamectl set-hostname redis-master

Slave — 192.168.1.102:

sudo hostnamectl set-hostname redis-slave

Verify:

hostname

---

2. Configure /etc/hosts

On both servers:

sudo nano /etc/hosts

Add:

192.168.1.101 redis-master
192.168.1.102 redis-slave

Test connectivity:

From Master:

ping -c 3 redis-slave

From Slave:

ping -c 3 redis-master

Both should work.

---

3. Install Redis

Run on both servers:

sudo apt update
sudo apt install redis-server -y

Check Redis version:

redis-server --version

Check service:

sudo systemctl status redis-server

You should see:

Active: active (running)

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4. Configure Redis Master

On 192.168.1.101:

Open the Redis configuration:

sudo nano /etc/redis/redis.conf

Find:

bind 127.0.0.1 -::1

Change it to:

bind 0.0.0.0

For production, bind only to the required private interface/IP instead of 0.0.0.0.

Find:

protected-mode yes

Keep it as:

protected-mode yes

Find:

# requirepass foobared

For this lab, leave authentication disabled. For production, enable a strong password/ACL.

Save: Ctrl + O → Enter → Ctrl + X

Restart Redis:

sudo systemctl restart redis-server

Check:

sudo systemctl status redis-server

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5. Test the Redis Master

On 192.168.1.101:

redis-cli

Run:

PING

Expected:

PONG

Create test data:

SET message "Hello from Redis Master"

Expected:

OK

Check it:

GET message

Expected:

"Hello from Redis Master"

Exit:

exit

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6. Configure Redis Replica

Now go to 192.168.1.102:

sudo nano /etc/redis/redis.conf

Find:

bind 127.0.0.1 -::1

Change to:

bind 0.0.0.0

Then find the replica configuration. Depending on the Redis version, you may see:

# replicaof <masterip> <masterport>

Change it to:

replicaof 192.168.1.101 6379

Save: Ctrl + O → Enter → Ctrl + X

Restart Redis:

sudo systemctl restart redis-server

Check:

sudo systemctl status redis-server

---

7. Check Replica Status

On the replica:

redis-cli

Run:

INFO replication

Look for:

role:slave
master_host:192.168.1.101
master_port:6379
master_link_status:up

Depending on your Redis version, role may be shown as role:replica.

The important part is:

master_link_status:up

Exit:

exit

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8. Test Replication

Now we’ll test whether data created on the master appears on the replica.

On Master

Connect:

redis-cli

Run:

SET username "admin"

Then:

GET username

Expected:

"admin"

On Replica

Connect to the replica:

redis-cli

Run:

GET username

Expected:

"admin"

Replication is working.

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9. Test Automatic Data Replication

On the Master:

redis-cli

Run:

SET server "redis-master"
SET environment "testing"
SET application "my-app"

Then on the Replica:

redis-cli

Run:

GET server
GET environment
GET application

Expected:

"redis-master"
"testing"
"my-app"

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10. Important: Replica Is Read-Only

By default, a Redis replica does not accept normal writes.

On the replica, try:

SET test "hello"

You should get an error:

READONLY You can't write against a read only replica.

This confirms that the replica is operating as a read-only replica.

---

11. Check Replication from the Master

On the master:

redis-cli INFO replication

You should see:

role:master
connected_slaves:1
slave0:ip=192.168.1.102,port=6379,state=online

On newer Redis versions, you may see replica0 terminology instead.

The important values are:

Value	Expected
role	master
connected_slaves	1
state	online

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12. Configure Firewall

If UFW is enabled, allow Redis only from the replica.

On the Master:

sudo ufw allow from 192.168.1.102 to any port 6379 proto tcp

Check:

sudo ufw status

Do not expose Redis port 6379 to the public internet.

---

13. Test Network Connectivity

From the replica:

nc -zv 192.168.1.101 6379

Expected:

Connection to 192.168.1.101 6379 port [tcp/redis] succeeded!

If nc isn’t installed:

sudo apt install netcat-openbsd -y

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14. Test Replication After Restart

Restart the master:

sudo systemctl restart redis-server

Wait a few seconds.

On the replica:

redis-cli INFO replication

Check:

master_link_status:up

Then test:

redis-cli GET username

The data should still be available.

---

15. Important Limitation

With this setup:

Master (192.168.1.101)
    │
    ▼
Replica (192.168.1.102)

If the master goes down, the replica does not automatically become the master.

For automatic failover, you need Redis Sentinel.

The production architecture would look like:

                 Redis Sentinel
                       │
          ┌────────────┴────────────┐
          │                         │
          ▼                         ▼
   Redis Master              Redis Replica
   192.168.1.101             192.168.1.102

With Sentinel, if the master fails, Sentinel can promote the replica.

---

16. Useful Commands

Command	Purpose
sudo systemctl status redis-server	Check Redis service
sudo systemctl restart redis-server	Restart Redis
redis-server --version	Check Redis version
redis-cli PING	Test Redis
redis-cli INFO replication	Check replication
redis-cli INFO	Check all Redis information
redis-cli MONITOR	Monitor Redis commands (Ctrl+C to stop)

---

17. Final Architecture

┌──────────────────────────────┐
│       Redis Master           │
│                              │
│ IP: 192.168.1.101            │
│ Port: 6379                   │
│ Role: Master/Primary         │
└──────────────┬───────────────┘
               │
               │ Replication
               │
               ▼
┌──────────────────────────────┐
│       Redis Replica          │
│                              │
│ IP: 192.168.1.102            │
│ Port: 6379                   │
│ Role: Replica                │
│ Read-only                    │
└──────────────────────────────┘

Verification Checklist

• Redis installed on both servers
• Master running on 192.168.1.101
• Replica running on 192.168.1.102
• Replica connected to master
• master_link_status:up
• connected_slaves:1
• Data replicated from master to replica
• Replica is read-only

Next recommended step: Add Redis Sentinel to these two servers (plus a third Sentinel node for reliable quorum). That gives you automatic master failover instead of just replication.

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Conclusion

You have successfully set up Redis master-replica replication on Ubuntu 24.04. The replica continuously syncs data from the master and serves read requests, which helps scale read-heavy workloads. For production use, consider adding Redis Sentinel for automatic failover and enabling authentication for security.