So far, we've talked quite a bit about managing data within single machines, though with one or more cores. This is complicated enough as is. Preventing race conditions and deadlocks can be hard to begin with, but what happens when you introduce more machines (virtual or real) to the mix?

The first thing that should come to mind is that you can throw out a lot of the inherent tools that Go provides, and to a large degree that's true. You can mostly guarantee that Go can handle internal locking and unlocking of data within its own, singular goroutines and channels, but what about one or more additional instances of an application running? Consider the following model:

Here we see that either of these threads across either process could be reading from or writing to our Critical Data at any given point. With that in mind, there exists a need to coordinate access to that data.

At a very high level, there are two direct strategies for handling this, a distributed lock or consistency hash table (consistent hashing).

The first strategy is an extension of mutual exclusions except that we do not have direct and shared access to the same address space, so we need to create an abstraction. In other words, it's our job to concoct a lock mechanism that's visible to all available external entities.

The second strategy is a pattern designed specifically for caching and cache validation/invalidation, but it has relevancy here as well, because you can use it to manage where data lives in the more global address space.

However, when it comes to ensuring consistency across these systems, we need to go deeper than this general, high-level approach.

Split this model down the middle and it becomes easy: channels will handle the concurrent flow of data and data structures, and where they don't, you can use mutexes or low-level atomicity to add additional safeguards.

However, look to the right. Now you have another VM/instance or machine attempting to work with the same data. How can we make sure that we do not encounter reader/writer problems?