Let's continue to resiliency. You're waiting on the line for 10 minutes, then the line drops. Or, you reached one of the customer care representatives, but they hang up on you by mistake. How often does that happen? That's the system not being resilient to failures. Or, you've waited in line for half an hour to see a doctor, when they suddenly leave the office and go to a golf club, asking you to come back tomorrow. That's a system that wasn't responsive in the face of failure. 

The reactive manifesto discusses various ways to achieve resiliency:

• Delegation
• Replication
• Containment
• Isolation

Delegation is when the doctor comes out of their office and tells you, I can't see you today, but knock on the other door; they'll see to you soon.

Replication is for a clinic to always have two doctors available, just in the event that one of them miss their favorite team playing this evening. It relates to elasticity, which we'll discuss in the next section.

Containment and isolation are usually discussed together. What if you actually don't need to see the doctor? Maybe you only need a prescription from them. Then, you could leave them a message (we'll discuss message-passing soon, as it's also an important part of reactiveness) and they'll send you a recipe when they're between games. You decoupled yourself from seeing a doctor. It also provided you with isolation from the doctors' failures or problems. What you didn't know is that, while printing your recipe, their computer crashed twice and they were really stressed about that. But because you weren't in front of them, they kept that to themselves.