Installing and Configuring Redis

In order to get the latest version of Redis, we will use apt to install it from the official Debian repositories.
Update your local apt package cache and install Redis by typing:

apt update
apt install redis-server

This will download and install Redis and its dependencies.
Open this file with your preferred text editor:

vi /etc/redis/redis.conf

Inside the file, find the supervised directive. This directive allows you to declare an init system to manage Redis as a service, providing you with more control over its operation. The supervised directive is set to no by default. Since you are running Debian, which uses the systemd init system, change this to systemd:

vi /etc/redis/redis.conf
. . .
# If you run Redis from upstart or systemd, Redis can interact with your
# supervision tree. Options:
#   supervised no      - no supervision interaction
#   supervised upstart - signal upstart by putting Redis into SIGSTOP mode
#   supervised systemd - signal systemd by writing READY=1 to $NOTIFY_SOCKET
#   supervised auto    - detect upstart or systemd method based on
#                        UPSTART_JOB or NOTIFY_SOCKET environment variables
# Note: these supervision methods only signal "process is ready."
#       They do not enable continuous liveness pings back to your supervisor.
supervised systemd
. . .

That’s the only change you need to make to the Redis configuration file at this point, so save and close it when you are finished.
Reload the Redis service to reflect the changes you made to the configuration file:

systemctl restart redis

Testing Redis

Start by checking that the Redis service is running:

systemctl status redis

If it is running without any errors, this command will produce output similar to the following:

Output
● redis-server.service - Advanced key-value store
Loaded: loaded (/lib/systemd/system/redis-server.service; enabled; vendor preset: enabled)
Active: active (running) since Wed 2021-02-11 20:19:44 UTC; 41s ago
    Docs: http://redis.io/documentation,
        man:redis-server(1)
Process: 10829 ExecStopPost=/bin/run-parts --verbose /etc/redis/redis-server.post-down.d (code=exited, status=0/SUCCESS)
Process: 10825 ExecStop=/bin/kill -s TERM $MAINPID (code=exited, status=0/SUCCESS)
Process: 10823 ExecStop=/bin/run-parts --verbose /etc/redis/redis-server.pre-down.d (code=exited, status=0/SUCCESS)
Process: 10842 ExecStartPost=/bin/run-parts --verbose /etc/redis/redis-server.post-up.d (code=exited, status=0/SUCCESS)
Process: 10838 ExecStart=/usr/bin/redis-server /etc/redis/redis.conf (code=exited, status=0/SUCCESS)
Process: 10834 ExecStartPre=/bin/run-parts --verbose /etc/redis/redis-server.pre-up.d (code=exited, status=0/SUCCESS)
Main PID: 10841 (redis-server)
    Tasks: 3 (limit: 4915)
CGroup: /system.slice/redis-server.service
       └─10841 /usr/bin/redis-server 127.0.0.1:6379

Here, you can see that Redis is running and is already enabled,

To test that Redis is functioning correctly, connect to the server using the command-line client:

redis-cli

In the prompt that follows, test connectivity with the ping command:

ping 

Output
PONG

This output confirms that the server connection is still alive. Next, check that you’re able to set keys by running:

set test "It's working!"

Output
OK

Retrieve the value by typing:

get test

Assuming everything is working, you will be able to retrieve the value you stored:

Output
"It's working!"

After confirming that you can fetch the value, exit the Redis prompt to get back to the shell:

exit

As a final test, we will check whether Redis is able to persist data even after it’s been stopped or restarted.
To do this, first restart the Redis instance:

systemctl restart redis

Then connect with the command-line client once again and confirm that your test value is still available:

redis-cli
get test

The value of your key should still be accessible:

Output
"It's working!"

Exit out into the shell again when you are finished:

exit

Binding to localhost

By default, Redis is only accessible from localhost.
However, if you installed and configured Redis to server applications outside your server, you might have updated the configuration file to allow connections from anywhere.
This is not as secure as binding to localhost.

To correct this, open the Redis configuration file for editing:

vi /etc/redis/redis.conf

Locate this line and make sure it is uncommented (remove the # if it exists):
/etc/redis/redis.conf

bind 127.0.0.1 # allow connection only from localhost.
#bind 127.0.0.1 # allow connection from outside.

Save and close the file when finished (press :wq then ENTER).

Then, restart the service to ensure that systemd reads your changes:

systemctl restart redis

To check that this change has gone into effect, run the following netstat command:

sudo netstat -lnp | grep redis

Output
tcp 0 0 127.0.0.1:6379 0.0.0.0:* LISTEN 10959/redis-server

This output shows that the redis-server program is bound to localhost (127.0.0.1), reflecting the change you just made.

Configuring a Redis Password

Configuring a Redis password enables one of its two built-in security features — the auth command, which requires clients to authenticate to access the database.
The password is configured directly in Redis’s configuration file, /etc/redis/redis.conf, so open that file again with your preferred editor:

vi /etc/redis/redis.conf

Scroll to the SECURITY section and look for a commented directive that reads:
/etc/redis/redis.conf

#requirepass password_of_your_choice

Uncomment it by removing the #, and change password_of_your_choice to a secure password.

Note: Above the requirepass directive in the redis.conf file, there is a commented warning:
Warning: since Redis is pretty fast an outside user can try up to
150k passwords per second against a good box. This means that you should
use a very strong password otherwise it will be very easy to break.

It’s important that you specify a very strong and very long value as your password.
Rather than make up a password yourself, you can use the openssl command to generate a random one, as in the following example.
By piping the output of the first command to the second openssl command, as shown here, it will remove any line breaks produced by that the first command:

openssl rand 60 | openssl base64 -A

Your output should look something like:

Output
RBOxxxxxoGCKhlEBwQLHri1g+atWgn4Xn4HwNUbtzoVxAYxkiYBi7aufl4MILv1nxBqR4L6NNzI0X6cE

After copying and pasting the output of that command as the new value for requirepass, it should read:
/etc/redis/redis.conf

requirepass RBOxxxxxoGCKhlEBwQLHri1g+atWgn4Xn4HwNUbtzoVxAYxkiYBi7aufl4MILv1nxBqR4L6NNzI0X6cE

After setting the password, save and close the file, then restart Redis:

systemctl restart redis.service

To test that the password works, access the Redis command line:

redis-cli

The following shows a sequence of commands used to test whether the Redis password works. The first command tries to set a key to a value before authentication:

set key1 10

That won’t work because you didn’t authenticate, so Redis returns an error:

Output
(error) NOAUTH Authentication required.

The next command authenticates with the password specified in the Redis configuration file:

auth your_redis_password

Redis acknowledges:

Output
OK

After that, running the previous command again will succeed:

set key1 10

Output
OK

get key1 queries Redis for the value of the new key.

get key1

Output
"10"

After confirming that you’re able to run commands in the Redis client after authenticating, you can exit the redis-cli:

quit

Next, we’ll look at renaming Redis commands which, if entered by mistake or by a malicious actor, could cause serious damage to your machine.

Renaming Dangerous Commands

The other security feature built into Redis involves renaming or completely disabling certain commands that are considered dangerous.

When run by unauthorized users, such commands can be used to reconfigure, destroy, or otherwise wipe your data. Like the authentication password, renaming or disabling commands is configured in the same SECURITY section of the /etc/redis/redis.conf file.

Some of the commands that are considered dangerous include: FLUSHDB, FLUSHALL, KEYS, PEXPIRE, DEL, CONFIG, SHUTDOWN, BGREWRITEAOF, BGSAVE, SAVE, SPOP, SREM, RENAME, and DEBUG. This is not a comprehensive list, but renaming or disabling all of the commands in that list is a good starting point for enhancing your Redis server’s security.

Whether you should disable or rename a command depends on your specific needs or those of your site. If you know you will never use a command that could be abused, then you may disable it. Otherwise, it might be in your best interest to rename it.

To enable or disable Redis commands, open the configuration file once more:

vi /etc/redis/redis.conf

Warning:
The following steps showing how to disable and rename commands are examples. You should only choose to disable or rename the commands that make sense for you. You can review the full list of commands for yourself and determine how they might be misused at redis.io/commands.

To disable a command, simply rename it to an empty string (signified by a pair of quotation marks with no characters between them), as shown below:
/etc/redis/redis.conf

# It is also possible to completely kill a command by renaming it into
# an empty string:
#
rename-command FLUSHDB ""
rename-command FLUSHALL ""
rename-command DEBUG ""

To rename a command, give it another name as shown in the examples below. Renamed commands should be difficult for others to guess, but easy for you to remember:
/etc/redis/redis.conf

# rename-command CONFIG ""
rename-command SHUTDOWN SHUTDOWN_MENOT
rename-command CONFIG ASC12_CONFIG

Save your changes and close the file.

After renaming a command, apply the change by restarting Redis:

systemctl restart redis

To test the new command, enter the Redis command line:

redis-cli

Then, authenticate:

auth your_redis_password

Output
OK

Let’s assume that you renamed the CONFIG command to ASC12_CONFIG, as in the preceding example. First, try using the original CONFIG command.
It should fail, because you’ve renamed it:

config get requirepass

Output
(error) ERR unknown command 'config'

Calling the renamed command, however, will be successful. It is not case-sensitive:

asc12_config get requirepass

Output
1) "requirepass"
2) "your_redis_password"

Finally, you can exit from redis-cli:

exit

Note that if you’re already using the Redis command line and then restart Redis, you’ll need to re-authenticate. Otherwise, you’ll get this error if you type a command:

Output
NOAUTH Authentication required.

Regarding the practice of renaming commands, there’s a cautionary statement at the end of the SECURITY section in /etc/redis/redis.conf which reads:

Please note that changing the name of commands that are logged into the AOF file or transmitted to slaves may cause problems.

Note: The Redis project chooses to use the terms “master” and “slave” while DigitalOcean generally prefers alternative descriptors. In order to avoid confusion we’ve chosen to use the terms used in the Redis documentation here.

That means if the renamed command is not in the AOF file, or if it is but the AOF file has not been transmitted to slaves, then there should be no problem.

So, keep that in mind when you’re trying to rename commands. The best time to rename a command is when you’re not using AOF persistence, or right after installation, that is, before your Redis-using application has been deployed.

When you’re using AOF and dealing with a master-slave installation, consider this answer from the project’s GitHub issue page. The following is a reply to the author’s question:

The commands are logged to the AOF and replicated to the slave the same way they are sent, so if you try to replay the AOF on an instance that doesn’t have the same renaming, you may face inconsistencies as the command cannot be executed (same for slaves).

Thus, the best way to handle renaming in cases like that is to make sure that renamed commands are applied to all instances in master-slave installations.