I have a web application spread over multiple servers and the incoming traffic is handled by HAProxy in order to balance the load. When we do the distribution, we do it at night because the users are much less and therefore we are less in service. To make the distribution we use the following strategy:
we shut down half of the servers
we deploy on servers that are turned off
we reactivate the servers that are turned off
we perform the same procedure on the other servers
The problem is that in any case I turn off the servers we close connections to users. Is there a better strategy for doing this? How could I improve this and avoid disservices and maybe be able to make distributions even during the day?
I hope I was clear. Thanks
I strongly suggest to use health checks for the servers.
Using HAProxy as an API Gateway, Part 3 [Health Checks]
You should have a URL ("/health") which you can use for health check of the backend server and add option redispatch to the config.
Now when you want to maintain the backend server just "remove" the "/health" URL and haproxy automagically routes the user to the other available servers.
I have one Batch job on one server which is intern calling the service on the other server.
The issue is-(we suspect)the batch job is unable to call the service,but we are not very sure.
How to ensure that service is not getting called from the network point of view.
we checked telnet between the two servers which is fine.
Is this the only way to troubleshoot?
note: we can not do the code level changes now.
You could make use of tools like wireshark or
tcpdump to capture the network traffic and see that your script is indeed sending o/g requests.
I have just created zend project on my local machine. but when I try to run it in the browser, it just loads for at least a minute and then shows this error.
Fatal error: Maximum execution time of 30 seconds exceeded in /opt/lampp/htdocs/launchmind/library/Zend/Db/Adapter/Abstract.php on line 815
It displays the same error with some other line number on some other file every time I reload the page.
Please help. Thank you.
Most likely you have some firewall issue that causes the script to timeout. Check connections from you local machine to all the database hosts in the config and/or webservices and/or other involved servers.
Here are few tips:
Monitor xampp error_log and /var/log/messages...
Since it's local server, disable the firewall temporarily to see if the problem is with your local firewall (preventing outgoing connection) or remote server firewall (preventing incoming connection). On RHEL use sudo service iptables stop or /etc/init.d/iptables stop
if you have very time consuming tasks in your app (very unlikely) then you can try to bump up the max execution time either by modifying /opt/lampp/etc/php.ini (somewhere there) or set max execution time in your app config phpSettings.max_execution_time = 60 or use ini_set in bootstrap
Hope this helps.
I am having a server client application developed in vb.net. The server app sends a file to the client app at regular intervals. It uses TCP/IP to send files.
After installing the application the application runs fine with firewall off. But when firewall is on and an exception is added for the application, the file transfer works for around 10 mins and then stops.
But as soon as i turn off the firewall, the transfer starts again. Please suggest how to resolve this issue.
When you say "file transfer works for around 10 mins and then stops" can you elaborate a little more. For example... "I am transferring a large file and during the transfer, it stops." or "I transferred a file successfully, and ten minutes later, went to transfer another, and it didn't work."
In the first scenario (large transfer), there may be some form of bandwidth limitation/rule stopping. In the second, there could be some form of "STATE" processing where a STATEFUL session occurs, the firewall doesn't close it, another initiation is made 10 minutes later, and your firewall is viewing the session "someone is trying to piggyback/hijack this session... better close it"
I would turn on verbose logging on the firewall to see what the firewall is doing and how it perceives the connection.
Does anyone have experience deploying GWT apps to EC2?
If I were to install tomcat or apache on a ec2 instance, could I have users connect directly to a url pointing there?
Would that be cost effective, or would java hosting services be best?
Is there any downside to hosting the edge HTTP server on a regular hosting service and have that direct requests to EC2? Performance ever an issue here?
Other answers are correct but I just wanted to share the fact that we are are developing a product that is 100% EC2/S3 based and also have a pure GWT front end.
We use maven2 for builds and the excellent gwt-maven plugin. This makes it easy to produce a WAR package of our web application as output. We use Jetty but Tomcat would work just as well.
We have pound (a http accelerator/load balancer) running on the VM listening for http & https, which then forwards to requests to lighttpd (static) or jetty (app). This also simplifies SSL certificates because pound handles SSL. I've found Java servers have always been a pain to configure with SSL certs.
Yes, you can host pretty much whatever you want, as you effectively have a dedicated Linux machine at your command.
As I last recall, the basic rate for an EC2 instance, on their "low end box" worked out to around $75/month, so you can use that as a benchmark against other vendors. That also assumed that the machine is up 24x7 (since you pay for it by the hour).
The major downside of an EC2 instance is simply that it can "go away" at any time, and when it does, any data written to your instance will "go away" as well.
That means you need to set it up so that you can readily restart the server, but also you need to offline any data that you generate and wish to keep (either to one of Amazons other services, like S3, or to some other external service). That will incur some extra costs depending on volume.
Finally, you will also be billed for any traffic to the service.
The thing to compare it against is another "Virtual Server" from some other vendor. There is a lot of interesting things that can be done with EC2, but it may well be easier to go with a dedicated Virtual hosting service if you're just using a single machine.
Others have given good answers. I would have to add that you need to spend programmer time getting to know EC2's quirks and addressing them (e.g. with EBS). It's not completely trivial, and though it is useful knowledge to have and may be worth it for that reason alone, if you want to get up and running quickly with just a few servers, you should probably look at other hosted options.
On the other hand, if you plan to scale up massively enough (eventually hosting many servers on EC2) then I would highly recommend it. You have to architect a few things, but you need to do that anyways. The flexibility of on-demand computing, and the generally low price, makes this a killer platform once you reach a certain scale of operation.
You definitely can host an http server in EC2, but you need to take into consideration the following:
As mentioned before the cost can be much higher than alternative hosting solutions
Your instance (the machine you've started in EC2) can go off unexpectedly. There is no guarantee from Amazon for 24x7 availability. This mean that the data you've stored in local storage will be lost and when you've start a new instance, it will get a new IP.
To successfully host a server in EC2, you therefore need to employ some other services from Amazon. You need Elastic IP, so that you can circumvent the new IP address problem. You can also use Elastic Block Storage. This is a service that will allow you to mount in your machine a disk, that will not go away when your instance is lost.