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My corporate website is going to change: the new one is ready on a different server. I have to put a countdown of 24 hours on the current site home page, at "hour 0" I will switch to the new website (IP address will be moved from the old server to the new one).

The current website daily traffic load peak is about 40req/sec. Switch is due at 9:00 am, at that time the load is usually 50% lower: max 20req/sec. The countdown does not refresh the page. Most of the traffic is done by anonymous users (90%). Here are current access statistics (1 month, Google Analytics): Sessions: 475.258 - Users: 151.132 - Page views: 1.611.529 - Pages/session: 3,39 - Avg. Session duration: 00:03:49 - Bounce rate: 50.38% - New sessions: 23.38%

Probably not useful, but for the sake of completeness my enviroment is a multitier installation of CMS Plone v.4.1.6: Frontend: Apache+Varnish Backend: 6 zeo clients (4x anonymous users, 2x authenticated users) OS: Debian 7 HW: 1VPS: 8GB RAM, 8 CPU (2,7GHz), 100GB DISK, 1Gb LAN

Is there a meaningful method to obtain an estimation of the load I have to deal with?

  • What time of day will the switch happen? Does your countdown automatically refresh the page at zero? Could you put something in your countdown to periodically ping analytics with an event so that you know how many users are watching it as it counts down? – Stephen Ostermiller Mar 17 '15 at 19:03
  • Thanks for point it out: switch is due at 9:00 am, at that time the load is usually 50% lower: max 20req/sec. The countdown does not refresh the page. Probably I can track users connected, but I need to estimate load a few days before the switch to properly reconfigure server, if needed. – Massimiliano De Ruosi Mar 19 '15 at 8:24
  • What kind of change is this? Is it a redesign? Is there lots of new functionality? What have you told users about what is changing? – Stephen Ostermiller Mar 19 '15 at 10:21
  • Yes, it is a redesign, with some new content area and a different navigation approach. We have done the switch and it turned out load did not change much: requests raised a little initially (+10% req/s), normalized after few minutes, with some bursts during the same day (+40% req/s) – Massimiliano De Ruosi Apr 17 '15 at 13:12
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The load will not change unless you did a big restructure, have untested functions/queries, and/or expect folks to horde the new site. The start load will be amplified but only to generate things like image caches (which you can do before the counter ends).

A good way to generate caches and do a basic load test is using something like Xenu. You can set it up to run multiple threads without throttling, or you can run it on multiple machines. The goal would be to crash your new site so let er rip along at a pace above your norm 40req/sec until you start encountering errors, 5xx, or query timeouts. By watching top in your *nix you can see what kind of averages are happening. You can then compare this side by side with your live top averages during the test(s). Remember you can press c while in top to expose paths to scripts. This may help clarify what is using what, when, and where.

There are also sweet load testeroos like loadimpact.com, but you gotta pay to get more crush. The free version of that app bursts from 5 to 40req/sec using something like 20 users. Xenu might stay "in pages" better too -- I see loadimpact requested assets and things (which is a significant less load than a full page request)

Finally, there is NewRelic which may help during the load tests and after the switch. You may be able to better monitor what is going on and it could alert you if SHTF some late night while you're all cozy in bed.

  • Thank you: Xenu and loadinpact are great hints: I will definitely dig in. NewRelic is also interesting, but we are already monitoring our infrastructure (using munin and nagios). By the way: we have done the switch and it turned out you were right: load did not change much. – Massimiliano De Ruosi Apr 17 '15 at 13:02

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