Capacity Management for Web Operations
John Allspaw Operations Engineering

the book I’m writing

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Rules of Thumb Planning/Forecasting Stupid
Capacity Tricks (with some Flickr statistics sprinkled in)

Things that can cause downtime
bugs (disguised as capacity problems) edge cases (disguised as capacity problems) security incidents real capacity problems* * (should be the last thing you need to worry about)

Capacity != Performance Forget about
performance for right now Measure what you have right NOW Don’t count on it getting any better

Thank You HPC Industry! Automated
Stuff Scalable Metric Collection/Display a lot of great deployment and management tricks come from them, adopted by web ops

Good Measurement Tools record and
store metrics in/out custom metrics easily compare lightweight-ish I

Clouds need planning too Makes
deployment and procurement easy and quick But clouds are still resources with costs and limits, just like your own stuff Black-boxes: you may need to pay even more attention than before

Metrics
System Statistics

Metrics “Application” Level (photos processed
per minute) (average processing time per photo) (apache requests) (concurrent busy apache procs)

Metrics App-level meets system-level here,
total CPU = ~1.12 * # busy apache procs (ymmv)

2400 photos per minute being
uploaded right NOW (Tuesday afternoon)

Ceilings the most amount of
“work” your resources will allow before degradation or failure

Forget Benchmarking

Find your ceilings what you
have left The End

Use real live production data
to find ceilings Production: “it’s like a lab, but bigger!”

Like: database ceilings replication lag:
bad!

Ceilings waiting on disk sustained
disk I/O wait for too much >40% creates slave lag* *for us,YMMV

35,000 photo requests per second
on a Tuesday peak

Safety Factors

Safety Factors Ceiling * Factor
of Safety = UR LIMITZ

Safety Factors
webserver!

Safety Factors what you have
left “safe” ceiling @85% CPU 85% total CPU = ~76 busy apache procs

Safety Factors Yahoo Front Page
link to Chinese NewYear Photos (8% spike) (photo requests/second)

Forecasting

Forecasting
Fictional Example:
webservers

Forecasting peak of the week
Fictional example: 15 webservers. 1 week.

Forecasting ...bigger sample, 6 weeks....isolate
the peaks...

Forecasting not too shabby now
...”Add a Trendline” with some decent correlation...

Forecasting this will tell you
when it is ceiling when is this? what you have left 15 servers @76 busy apache proc limit = 1140 total procs

Forecasting (1140-726) / 42.751 =
9.68 (week #10, duh)

Forecasting Automation Writing excel macros
is boring All we want is “days remaining”, so all we need is the curve-fit Use http://fityk.sf.net to automate the curve-fit

Forecasting
Fictional Example:
storage consumption

Forecasting Automation this will tell
you when this is actual flickr storage consumption from early 2005, in GB (ceiling is fictional)

Forecasting Automation jallspaw:~]$cfityk ./fit-storage.fit cmd
line script 1> # Fityk script. Fityk version: 0.8.2 output 2> @0 < '/home/jallspaw/storage-consumption.xy' 15 points. No explicit std. dev. Set as sqrt(y) 3> guess Quadratic New function %_1 was created. 4> fit Initial values: lambda=0.001 WSSR=464.564 #1: WSSR=0.90162 lambda=0.0001 d(WSSR)=-463.663 (99.8059%) #2: WSSR=0.736787 lambda=1e-05 d(WSSR)=-0.164833 (18.2818%) #3: WSSR=0.736763 lambda=1e-06 d(WSSR)=-2.45151e-05 (0.00332729%) #4: WSSR=0.736763 lambda=1e-07 d(WSSR)=-3.84524e-11 (5.21909e-09%) Fit converged. Better fit found (WSSR = 0.736763, was 464.564, -99.8414%). 5> info formula in @0 # storage-consumption 14147.4+146.657*x+0.786854*x^2 6> quit bye...

Forecasting Automation fityk gave: y
= 0.786854x2 + 146.657x + 14147.4 ( R2 = 99.84) Excel gave: y = 0.7675x2 + 146.96x + 14147.3 ( R2 = 99.84) (SAME)

Capacity Health 12,629 nagios checks
1314 hosts 6 datacenters 4 photo “farms” farm = 2 DCs (east/west)

High and Low Water Marks
alert if higher alert if lower Per server, squid requests per second

A good dashboard looks something
like... Est limit/ ceiling limit current % days type # box units (total) (peak) peak left busy www 20 80 1600 1000 62.50% 36 procs shard I/O 20 40 800 220 27.50% 120 db wait squid 18 950 req/sec 17,100 11,400 66.67% 48 (yes, fictional numbers)

Diagonal Scaling vertically scaling your
already horizontal nodes Image processing machines Replace Dell PE860s with HP DL140G3s

Diagonal Scaling example: image processing
4 cores 8 cores (about the same CPU “usage” per box)

Diagonal Scaling example: image processing
throughput ~45 images/min @ peak ~140 images/min @ peak (same CPU usage, but ~3x more work) “processing” means making 4 sizes from originals

Diagonal Scaling example: image processing
went from: 3008.4 1035 23U 23 Dell PE860s Watts photos/min rack to: 8 HP DL140 G3s 1036.8 Watts 1120 photos/min 8U rack !!! (75% faster, even)

3.52 terabytes will be consumed
today (on a Tuesday)

2nd Order Effects (beware the
wandering bottleneck) LB running hot, so add more www www db search memcached

2nd Order Effects (beware the
wandering bottleneck) LB running great now, so more traffic! now these run www www www www hot db search memcached

Stupid Capacity Tricks

Stupid Capacity Tricks quick and
dirty management DSH http://freshmeat.net/projects/dsh [root@netmon101 ~]# cat group.of.servers www100 www118 dbcontacts3 admin1 admin2

Stupid Capacity Tricks quick and
dirty management [root@netmon101 ~]# dsh -N group.of.servers dsh> date executing 'date' www100: Mon Jun 23 14:14:53 UTC 2008 www118: Mon Jun 23 14:14:53 UTC 2008 dbcontacts3: Mon Jun 23 07:14:53 PDT 2008 admin1: Mon Jun 23 14:14:53 UTC 2008 admin2: Mon Jun 23 14:14:53 UTC 2008 dsh>

Stupid Capacity Tricks Turn Stuff
OFF Disable heavy-ish features of the site (on/off switches) We have 195 different things to disable in case of emergency.

Stupid Capacity Tricks Turn Stuff
OFF uploads (photo) uploads (video) uploads by email various API things various mobile things various search things etc., etc.

Stupid Capacity Tricks Outages Happen
Host your outage/status/blog page in more than one datacenter. Tell your users WTF is going on, they’ll appreciate it.

Stupid Capacity Tricks Hit the
Pause Button Bake the dynamic into static Some Y! properties have a big red button to instantly bake (and un- bake) at will

thanks http://flickr.com/photos/bondidwhat/402089763/ http://flickr.com/photos/74876632@N00/2394833962/ http://flickr.com/photos/42311564@N00/220394633/ http://flickr.com/photos/unloveable/2422483859/
http://flickr.com/photos/absolutwade/149702085/ http://flickr.com/photos/krawiec/521836276/ http://flickr.com/photos/eschipul/1560875648/ http://flickr.com/photos/library_of_congress/2179060841/ http://flickr.com/photos/jekkyl/511187885/ http://flickr.com/photos/ab8wn/368021672/ http://flickr.com/photos/jaxxon/165559708/ http://flickr.com/photos/sparktography/75499095/

We’re Hiring! flickr.com/jobs Come see
me!

questions?