I need some guidance regarding an issue that comes up every now and then on AWS.
We have an instance hosting 2 applications which every now and then loses its connection with the EFS. This does not happen often but it happens 2 to 3 times a month. The logs only show that the fs-0000000.efs.us-east-1.amazonaws.com is not responding and then timed out.
Then it shows Unmounting /mnt/efs/servername. Further down the log it then shows mount: /mnt/efs/devserver/artifactory: unknown filesystem type 'efs'.
We then mount it again and it works fine till the next month. Any ideas what would cause this?
Any help would be appreciated.
Contacting AWS support, reading logs, troubleshooting AWS documentation and checking forums.
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We had few instances of our system on EC2. Some of them application servers, some of them Memcached, Database and etc.
After few weeks after creating instance, it starts to raise a lot number of errors depending to network: errors like "MEMCACHED TIMEOUT ERROR", "RABBITMQ connection error" and same. Errors happens only from single instance. After creating copy of this instance - errors goes away.
Did anybody have same problems?
I have experienced this before. I think it has to do with problems with the network stack of the host, at least that is as much information I could get form aws.
If you are using EBS backed instances. Simply stopping and then restarting the instance should solve the problem. The instance gets assigned to a new host in that case.
I'va have my web hosted via a Amazon EC2.
Overall it's working fine, but sometimes (1 per hour aprox) it's like getting stuck. I'm not even able to write commands on the server console when it's on that status.
I moved from the micro instance to the small one expecting some improvement, but it's happening the same.
Any guidance where I should look to resolve this?
This depends on various factors.
Areas you should be looking:
If you are not able to connect (SSH) to your instance: check your
system log from your management console.
If you are expecting slow response times: check your CloudWatch metrics from your console.
Verify running processes on your instance. find out which process is taking CPU % / Memory %
you can do this by top or ps -auwx
EC2 dashboard mentions about a running instance, even when the instance is not running. I see a EBS volume also in a in-use status. I am confused, is the machine running or not?
I have seen that happen when closing down an linux instance on the machine (with shutdown now from the command line).
If the console says that the instance is running even though you shut it down you should probably shut it down from the console (to avoid being billed).
Sometimes there are problems with the hardware on the server. The instance is showing as running but you cannot connect and you cannot use any services on that instance. The best thing to do in this situation is post a message on EC2's forums and ask them to look at your instance.
They're usually pretty quick to respond though they don't make any grantees. They can force the machine into a stopped state, whether or not they can fix the issue without you loosing your data will depend on what is actually wrong with the instance.
This happens from time to time with my instances as well.
This problem appeared today and I have no idea what is going on. Please share you ideas.
I have 1 EC2 DB server (MYSQL + NFS File Sharing + Memcached).
And I have 3 EC2 Web servers (lighttpd) where it will mounted the NFS folders on the DB server.
Everything going smoothly for months but suddenly there is an interesting phenomenon.
In every 8 minutes to 10 minutes, PHP file will be unreachable. This will last about 1 minute and then back to normal. Normal files like .html file are unaffected. All servers have the same problem exactly at the same time.
I have spent one whole day to analysis the reason. Finally, I find out when the problem appear, the file descriptor of lighttpd suddenly increased a lot.
I used ls /proc/1234/fd | wc -l to check the number of fd.
The # of fd is around 250 in normal time. However, when the problem appeared, it will be raised to 1500 and then back to normal.
It sounds funny, right? Do you have any idea what's going on?
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The CPU graph of one of the web server.
alt text http://pencake.images.s3.amazonaws.com/4be1055884133.jpg
Thoughts:
Have a look at dmesg output.
The number of file descriptors jumping up sounds to me like something is blocking, including the processing of connections to the lighttpd/PHP, which builds up untile the blocking condition ends.
When you say the PHP file is unreachable, do you mean the file is missing? Or maybe the PHP script stalls during execution or? What do the lihttpd log files say is happening on the calls to this PHP script. Are there any other hints in the lighttpd?
What is the maximum file descriptors for the process/user?
I and others have had bizarre networking behavior on EC2 instances from time to time. Give us more details on it. Maybe setup some additional monitoring of the connectivity between your instances. Consider moving your problem instance to another instance in the hopes of the problem magically disappearing. (Shot in the dark.)
And finally...
DOS attack? I doubt it--it would be offline or not. It is way too early in the debugging process for you to infere malice on someone elses part.
We're running a lightweight web app on a single EC2 server instance, which is fine for our needs, but we're wondering about monitoring and restarting it if it goes down.
We have a separate non-Amazon server we'd like to use to monitor the EC2 and start a fresh instance if necessary and shut down the old one. All our user data is on Elastic Storage, so we're not too worried about losing anything.
I was wondering if anyone has any experience of using EC2 in this way, and in particular of automating the process of starting the new instance? We have no problem creating something from scratch, but it seems like it should be a solved problem, so I was wondering if anyone has any tips, links, scripts, tutorials, etc to share.
Thanks.
You should have a look at puppet and its support for AWS. I would also look at the RightScale AWS library as well as this post about starting a server with the RightScale scripts. You may also find this article on web serving with EC2 useful. I have done something similar to this but without the external monitoring, the node monitored itself and shut down when it was no longer needed then a new one would start up later when there was more work to do.
Couple of points:
You MUST MUST MUST back up your Amazon EBS volume.
They claim "better" reliability, but not 100%, and it's SEVERAL orders of magnitude off of S3's "12 9's" of durability. S3 durability >> EBS durability. That's a fact. EBS supports a "snapshots" feature which backs up your storage efficiently and incrementally to S3. Also, with EBS snapshots, you only pay for the compressed deltas, which is typically far far less than the allocated volume size. In another life, I've sent lost-volume emails to smaller customers like you who "thought" that EBS was "durable" and trusted it with the only copy of a mission-critical database... it's heartbreaking.
Your Q: automating start-up of a new instance
The design path you mention is relatively untraveled; here's why... Lots of companies run redundant "hot-spare" instances where the second instance is booted and running. This allows rapid failover (seconds) in the event of "failure" (could be hardware or software). The issue with a "cold-spare" is that it's harder to keep the machine up to date and ready to pick up where the old box left off. More important, it's tricky to VALIDATE that the spare is capable of successfully recovering your production service. Hardware is more reliable than untested software systems. TEST TEST TEST. If you haven't tested your fail-over, it doesn't work.
The simple automation of starting a new EBS instance is easy, bordering on trivial. It's just a one-line bash script calling the EC2 command-line tools. What's tricky is everything on top of that. Such a solution pretty much implies a fully 100% automated deployment process. And this is all specific to your application. Can your app pull down all the data it needs to run (maybe it's stored in S3?). Can you kill you instance today and boot a new instance with 0.000 manual setup/install steps?
Or, you may be talking about a scenario I'll call "re-instancing an EBS volume":
EC2 box dies (root volume is EBS)
Force detach EBS volume
Boot new EC2 instance with the EBS volume
... That mostly works. The gotchas:
Doesn't protect against EBS failures, either total volume loss or an availability loss
Recovery time is O(minutes) assuming everything works just right
Your services need to be configured to restart automatically. It does no good to bring the box back if Nginx isn't running.
Your DNS routes or other services or whatever need to be ok with the IP-address changing. This can be worked around with ElasticIP.
How are your host SSH keys handled? Same name, new host key can break SSH-based automation when it gets the strong-warning for host-key-changed.
I don't have proof of this (other than seeing it happen once), but I believe that EC2/EBS _already_does_this_ automatically for boot-from-EBS instances
Again, the hard part here is on your plate. Can you stop your production service today and bring it up RELIABLY on a new instance? If so, the EC2 part of the story is really really easy.
As a side point:
All our user data is on Elastic Storage, so we're not too worried about losing anything.
I'd strongly suggest to regularly snapshot your EBS (Elastic Block Storage) to S3 if you are not doing that already.
You can use an autoscale group with a min/max/desired quantity of 1. Place the instance behind an ELB and have the autoscale group be triggered by the ELB healthy node count. This allows you to have built in monitoring by cloudwatch and the ELB health check. Anytime there is an issue the instance be replaced by the autoscale service.
If you have not checked 'Protect against accidental termination' you might want to do so.
Even if you have disabled 'Detailed Monitoring' for your instance you should still see the 'StatusCheckFailed' metric for your instance over which you can configure an alarm (In the CloudWatch dashboard)
Your application (hosted in a different server) should receive the alarm and start the instance using the AWS API (or CLI)
Since you have protected against accidental termination you would never need to spawn a new instance.