I have a windows based system that sits on an Amazon EC2 instance. There is a known issue that Windows EC2 instances have problems keeping their system time in sync. I'll randomly log into the system and find that my system clock is anywhere from a couple seconds off (not too big of a deal...) to several minutes or even hours off (obviously a huge deal). Considering that my site's prime objective is to issue out links to secured S3 content that is locked down by a considerably strict time limit (ie sometimes as little as 30 seconds to a minute), this is a huge issue for me. Scouring Amazon's help forums has yielded many answers that simply do not work and Amazon seems to be ignoring the issue claiming it's Windows related. Regardless, I've decided to take things into my own hands and not to wait on Amazon. Things I've considered: Creating a service that hits a list of time servers every hour or so, gets the current time, calculates the offset, and then uses this offset to generate accurate links. The downsides being that I need to have a substantial list of time servers so that they don't block me from hitting them too often. Also, if the time gets randomly fixed in the middle of one of these periods, my links will start breaking again. Creating a Linux EC2 instance and finding some way of getting its internal time. I haven't read anything on how accurate their times are within EC2, but I would have to assume it's better that this nonsense. Hosting my site elsewhere that has accurate clocks... Are there any other options you can think of that I may have missed? I'm not really opposed to anything with the one exception being rewriting my site in another language so as to move away from Windows (it's a .Net MVC application currently). Thanks in advance! EDIT: Also of note, I can not use referrer based security as the plugins I'm utilizing that use these links don't 100% send the referrer in some browsers.

Reputation: 3204

Dealing with an inaccurate system clock

I have a windows based system that sits on an Amazon EC2 instance. There is a known issue that Windows EC2 instances have problems keeping their system time in sync. I'll randomly log into the system and find that my system clock is anywhere from a couple seconds off (not too big of a deal...) to several minutes or even hours off (obviously a huge deal).

Considering that my site's prime objective is to issue out links to secured S3 content that is locked down by a considerably strict time limit (ie sometimes as little as 30 seconds to a minute), this is a huge issue for me. Scouring Amazon's help forums has yielded many answers that simply do not work and Amazon seems to be ignoring the issue claiming it's Windows related. Regardless, I've decided to take things into my own hands and not to wait on Amazon.

Things I've considered:

Creating a service that hits a list of time servers every hour or so, gets the current time, calculates the offset, and then uses this offset to generate accurate links. The downsides being that I need to have a substantial list of time servers so that they don't block me from hitting them too often. Also, if the time gets randomly fixed in the middle of one of these periods, my links will start breaking again.
Creating a Linux EC2 instance and finding some way of getting its internal time. I haven't read anything on how accurate their times are within EC2, but I would have to assume it's better that this nonsense.
Hosting my site elsewhere that has accurate clocks...

Are there any other options you can think of that I may have missed? I'm not really opposed to anything with the one exception being rewriting my site in another language so as to move away from Windows (it's a .Net MVC application currently).

Thanks in advance!

EDIT: Also of note, I can not use referrer based security as the plugins I'm utilizing that use these links don't 100% send the referrer in some browsers.

Upvotes: 5

Answers (4)

Arindam Nayak

Reputation: 7462

changed internet time server to "time.nist.gov", it corrected time.

Upvotes: 0

TomPed

Reputation: 1

I have been dealing with the same problem for weeks and found out the root of my problem was simple:

Make sure your Network ACL allows inbound UDP traffic.

Upvotes: 0

friism

Reputation: 19279

It's strange that your servers should drift several hours. By default, Windows Server 2008 R2 is configured to NTP-sync its clock with time.windows.com every 900 seconds (15 minutes). If this does not get you the required timeliness, you can increase the frequency by modifying a registry key.

If you're hosting a ASP.NET application, you should consider running it on AppHarbor. We run on top of of EC2, but take away dreary server management tasks like making sure clocks are in sync.

Upvotes: 3

totallyNotLizards

Reputation: 8569

you could try making an app on either your windows instance or a linux instance if you choose to go that way, and whenever you need to know what the time is send an api request to somewhere like this: http://worldtimeengine.com/api/ to get the current local time.

if you can't rely on the clock of the instance then get the time from somewhere else :)

Upvotes: 0

Dealing with an inaccurate system clock

Answers (4)

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