Azure Failure Was a Leap Year Glitch

judgecorp writes "Microsoft's Windows Azure cloud service was down much of yesterday, and the cause was a leap year bug as the service failed to handle the 29th day of February. Faults propagated making this a severe outage for many customers, including the UK Government's recently launched G-cloud service."

Comments

Some of the most common leap-year bugs

[tillerman35]

Some of the common leap year bugs that I've seen over the years:

1. A matrix with the number of days per month:
e.g. smallint dayspermonth[12]={31,28,31,30,31,30,31,31,30,31,30,31};
Indexing into the matrix for February (index 1) ignores leap years.

1. A matrix with 365 elements to represent a year's worth of something:
e.g. smallint hightemps[365];
This usually doesn't fail until Dec 31, when hightemp[mydate.dayofyear()-1] points to a non-existent element.
Of course, if dayofyear is calculated using the matrix in the prior bug, it will fail invisibly since that will be incorrect
as well.

2. Quck-n-dirty subtract one year math:
e.g. Convert date to char in YYYYDDMM format, convert char to int, subtract 10000, convert back to a char and then date.
Why people do this when you can dateadd(year,mydate,-1) is that easy, I have no clue. But it breaks horridly when
you use it to determine "one year ago today" from Feb 29.