Serviceability or maintainability is the ease with which you can replace or upgrade parts of your system without impacting the system as a whole.

Consider a situation where you must upgrade the operating system on one or more of your ordering service nodes, or if you need to replace a faulty peer within an organization. As with reliability or availability, having redundant (or parallel) resources to which application operations can be switched seamlessly is the way to handle this in an industrial-scale system. So-called Blue-Green deployment is one of the popular mechanisms used for this purpose. In a nutshell, you have two parallel environments (let's say, for the ordering service), one called Blue and one called Green, where the Blue environment is receiving live traffic. You can upgrade the operating systems on the Green machines, test them adequately, and then switch the traffic from Blue to Green. Now, while Green is serving requests, you can upgrade Blue in the same manner.

In a blockchain application with loosely coupled components, it is advisable to have Blue and Green environments for each of the components (orderers, peers, and MSPs) and carry out the upgrades and testing in stages, or one component cluster at a time, to minimize the chances of a mishap.