Stability

Define: transaction, system, resilience

a transaction is an abstract unit of work processed by the system.
a system is a collection of hosts, applications, network segments, power supplies... that process transactions from end to end
a resilient system keeps processing transactions, even when there are
- transient impulses (getting Slahdotted)
- persistent stresses (slow payment processing response)
- or component failures disrupting normal processing

Failure modes

failure mode: how system/components behave when they encounter a failure
safe failure modes that contain the damage and protect the rest of the system
resilient systems have designed failure modes

Cracks propagate

upstream errors can propage to downstream systems if they're not protected
example
- database exception because of failure ->
- exhausts database connection pool ->
- request handling threads become blocked waiting on connection ->
- whole system is down

Chain of Failure

the more tightly coupled the architecture, the greater the chance that this coding error can propagate
high levels of complexity provide more directions for the cracks to propagate in
tight coupling accelerates cracks