‘One of [the] purposes of monitoring systems was to provide data to allow us, as engineers, to detect patterns, and predict issues before they become production impacting. In order to do this, we need to be capturing data and storing it somewhere which allows us to analyse it. If we care about it – if the data could provide the kind of engineering insight which helps us to understand our systems and give early warning – we should be capturing it. ‘ …. ‘There are a couple of weaknesses in [Nagios’ design]. Assuming we’ve agreed that if we care about a metric enough to want to alert on it then we should be gathering that data for analysis, and graphing it, then we already have the data upon which to base our check. Furthermore, this data is not on the machine we’re monitoring, so our checks don’t in any way add further stress to that machine.’ I would add that if we are alerting on a different set of data from what we collect for graphing, then using the graphs to investigate an alarm may run into problems if they don’t sync up.
From JPL’s Laboratory for Reliable Software (LaRS). Great reference; there’s some really useful recommendations here, and good explanations of familiar ones like “prefer composition over inheritance”. Many are supported by FindBugs, too. Here’s the full list:
compile with checks turned on; apply static analysis; document public elements; write unit tests; use the standard naming conventions; do not override field or class names; make imports explicit; do not have cyclic package and class dependencies; obey the contract for equals(); define both equals() and hashCode(); define equals when adding fields; define equals with parameter type Object; do not use finalizers; do not implement the Cloneable interface; do not call nonfinal methods in constructors; select composition over inheritance; make fields private; do not use static mutable fields; declare immutable fields final; initialize fields before use; use assertions; use annotations; restrict method overloading; do not assign to parameters; do not return null arrays or collections; do not call System.exit; have one concept per line; use braces in control structures; do not have empty blocks; use breaks in switch statements; end switch statements with default; terminate if-else-if with else; restrict side effects in expressions; use named constants for non-trivial literals; make operator precedence explicit; do not use reference equality; use only short-circuit logic operators; do not use octal values; do not use floating point equality; use one result type in conditional expressions; do not use string concatenation operator in loops; do not drop exceptions; do not abruptly exit a finally block; use generics; use interfaces as types when available; use primitive types; do not remove literals from collections; restrict numeric conversions; program against data races; program against deadlocks; do not rely on the scheduler for synchronization; wait and notify safely; reduce code complexity
Links for 2013-03-25
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