Question: How can you scale Memcached horizontally?

Answer

Scaling Memcached horizontally involves adding more servers to your Memcached cluster, allowing the system to distribute the load across multiple machines. This increases cache space and distributes the processing load, improving the system's overall capacity and performance.

Here are the steps to do that:

1. Setup New Memcached Server Instances: Begin by setting up new instances of Memcached servers on separate hardware machines or virtual machines. Make sure they're configured properly and are running efficiently.

sudo apt update
sudo apt install memcached

2. Configure Your Client to Connect to All Servers: After setting up your Memcached servers, configure your client application to connect to all these servers. The way you do this depends on the client library used in your application.

If you're using the python-memcached client, for instance, it would look something like this:

import memcache

servers = ['192.168.1.1:11211', '192.168.1.2:11211', '192.168.1.3:11211']
mc = memcache.Client(servers)

mc.set('key', 'value')
print(mc.get('key'))

In this example, 192.168.1.1, 192.168.1.2, and 192.168.1.3 are the IP addresses of your Memcached servers. Note that you need to replace them with the actual IP addresses of your machines.

3. Distribute Data Among Servers: Memcached clients usually use a consistent hashing algorithm to distribute data among different servers. When a new server is added, only a minimal amount of keys are remapped to the new server, which reduces the impact on cache effectiveness.

Remember, horizontal scaling requires management of the server pool and proper distribution of cached objects. It's also important to note that Memcached does not sync data between different servers - if one server fails, the data contained within it will be lost until it's repopulated. Therefore, Memcached should only be used to cache data that can be regenerated or re-queried from a persistent storage layer.

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