Is Redis needed with such architecture? Why is it used here?

Redis is often used as a high-performance cache or message broker in application architecture. If your architecture involves tasks that require quick access to data that is frequently read and rarely changed, Redis can significantly reduce the load on the primary database.

Additionally, Redis is useful for implementing task queues, user sessions, distributed locks, and other scenarios where speed and atomicity of operations are important.

Example of using Redis for caching in Java with Jedis:

try (Jedis jedis = new Jedis("localhost")) {
    String value = jedis.get("key");
    if (value == null) {
        value = loadFromDatabase("key");
        jedis.set("key", value);
    }
    System.out.println(value);
}

If your architecture does not have such requirements and all data is processed directly in the database or another storage with acceptable performance, then Redis may be redundant.