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+## Overview
+Distributed locks are a very useful primitive in many environments where different processes must operate with shared resources in a mutually exclusive way.
+
+## Safety property: 
+Mutual exclusion. At any given moment, only one client can hold a lock.
+## Liveness property A: 
+Deadlock free. Eventually it is always possible to acquire a lock, even if the client that locked a resource crashes or gets partitioned.
+## Liveness property B: 
+Fault tolerance. As long as the majority of Redis nodes are up, clients are able to acquire and release locks.
+
+## Implementation
+Before trying to overcome the limitation of the single instance setup described above, let’s check how to do it correctly in this simple case, since this is actually a viable solution in applications where a race condition from time to time is acceptable, and because locking into a single instance is the foundation we’ll use for the distributed algorithm described here.
+
+To acquire the lock, the way to go is the following:
+```
+SET resource_name my_random_value NX PX 30000
+```
+The command will set the key only if it does not already exist (NX option), with an expire of 30000 milliseconds (PX option). The key is set to a value “myrandomvalue”. This value must be unique across all clients and all lock requests.
+
+Basically the random value is used in order to release the lock in a safe way, with a script that tells Redis: remove the key only if it exists and the value stored at the key is exactly the one I expect to be. This is accomplished by the following Lua script:
+
+```
+if redis.call("get",KEYS[1]) == ARGV[1] then
+    return redis.call("del",KEYS[1])
+else
+    return 0
+end
+```