We have a web service, which services both sets of higher priority and lower priority URLs and HAProxy is used for routing these requests to the web service.
Using a separate backend for these higher priority URLs and reserving servers only for this backend would be an under utilization of the servers, as these requests are low in number and infrequent. Is there a way to assign these higher priority URLs a higher weight in the backend queue, so that I don't want them to be waiting for long in the backend queue along with other lower priority URLs?
Looks like HAProxy team has released v1.9 with "Server Queue Priority Control", which pretty much does what is asked in this question. Cheers!
Source: https://www.haproxy.com/blog/haproxy-1-9-has-arrived/
Related
Suppose we establish a WebRTC conference among A, B & C. Then will there be A <--> B, A <--> C, B <--> C individual calls?
Qn-1: If yes, then isn't that inefficient? Because each peer uploads the same data twice.
Now, Google has a different strategy for conferences. In their official document, it reads:
Does classic Hangouts use peer-to-peer calling for a Hangout with more than two participants?
Peer-to-peer connections are used only for calls with two participants. If any additional participants join, classic Hangouts will immediately go back to sending and receiving data using the connection to the Google server.
Qn-2: Now suppose if we go with p2p approach nevertheless. Now somehow we route all the traffic to one single port. Then is there any WebRTC limitation on how many connections can it make at a same time to a same IP and same port?
The reason for above question is that, if we do that with some hacks then after 4 outgoing connections, the 5th connection will always be unstable and mostly fail.
There is enough material to suggest that the P2P based "Mesh" network is suitable for up to 4 user stable conference.
This video states that "Mesh" network is the most naive way to implement a conference
This link suggests that the bandwidth is overwhelmed and the quality reduces as the participants increase in P2P:
In this link, it states that "Mesh" network starts failing as the number of participants increase.
Due to rising server load from DOS attacks I've decided to use Cloudflare, but I am aware their users suffered an hours outage in March because all Cloudflare Name Servers were "down".
I have my own NS, can I retain this as NS3 for the domain (for fallback) alongside Cloudflares "NS1 & NS2"?
What would the impact be?
I am aware Nameservers aren't selected in number order but I believe it is likely that Cloudflares commonly used NS in the client's locale are likely to be selected first - so only a small portion of traffic would use my NS3 (without the benefits of Cloudflare services). Is this correct or just wishfull thinking on my part?
Please do consider opening a support ticket for these kind of questions at CloudFlare directly.
You won't be able to leave additional name servers in place, as in ns3 and n4 -- in addition to the 2 provided CloudFlare name servers. To use our service you'd need to only have our 2 name servers in place.
Your assumption is correct, 33% of traffic will be served by your NS.
You can TCP/UDP stream proxy with n* nginx/haproxy/dnsmasq to n* NS backend to load balance incoming requests.
I tested several dnsmasq scenarios, you can serve 15k r/s with a simple Celeron up to 150k r/s with redundant, cheap, geo distributed VPSes. You can also use AWS Route53 to have solid perfs.
In addition to that you can spin up n* nginx proxy manager instances with WAF enabled and SSL wildcard certificates to match most of the "Cloudflare edge logic" and protect/mask your origin ip addresses even if 1/3rd of the clients resolves origins from your own NS.
I have been asked to set up some registration forms for clients that will take payments, similar to this site (https://www.martialartstechnologies.com/register?tournamentID=82). I am a reseller for Authorize.net, but I find it hard to sign clients up sometimes after they find out they need to get PCI compliant. I was thinking of creating one site domain that is PCI Compliant and then running each clients registration page in their own personal subdomain. If I do this, will the PCI compliance on the domain become invalid for each subdomain, or will it still be covered?
Only company can be PCI compliant, not a server, a site, a particular script, a domain or subdomain name. Whole infrastructure, including such things as office WiFi networks and cabinet locks is being audited. You can't trick the auditor painting a cabinet in a different color and claiming it is not yours.
Even if you got 1000 domain names - and they are pointed to 1000 servers located in 1000 places all over the Earth - you must list them all for PCI audit and make them all PCI compliant.
Subdomains can be on different servers, so the first question to answer would be 'same or different servers'? If on different servers and handling credit card info, you would need to make each server PCI compliant regardless.
PCI compliance deals with the question of code/infrastructure.
You cannot, as suggested, automatically extend it to sub-domains - even if the main domain is compliant.
Still, if you use the same infrastructure for all sub-domain, you can take care of code related vulnerabilities or just envelope the whole structure in a PCI DDS compliant WAF (I suggest Cloud PCI DDS compliant WAF to cut costs).
I am curious if anyone has any information about the scalability of HTML WebSockets. For everything I've read it appears that every client will maintain an open line of communication with the server. I'm just wondering how that scales and how many open WebSocket connections a server can handle. Maybe leaving those connections open isn't a problem in reality, but it feels like it is.
In most ways WebSockets will probably scale better than AJAX/HTML requests. However, that doesn't mean WebSockets is a replacement for all uses of AJAX/HTML.
Each TCP connection in itself consumes very little in terms server resources. Often setting up the connection can be expensive but maintaining an idle connection it is almost free. The first limitation that is usually encountered is the maximum number of file descriptors (sockets consume file descriptors) that can be open simultaneously. This often defaults to 1024 but can easily be configured higher.
Ever tried configuring a web server to support tens of thousands of simultaneous AJAX clients? Change those clients into WebSockets clients and it just might be feasible.
HTTP connections, while they don't create open files or consume port numbers for a long period, are more expensive in just about every other way:
Each HTTP connection carries a lot of baggage that isn't used most of the time: cookies, content type, conetent length, user-agent, server id, date, last-modified, etc. Once a WebSockets connection is established, only the data required by the application needs to be sent back and forth.
Typically, HTTP servers are configured to log the start and completion of every HTTP request taking up disk and CPU time. It will become standard to log the start and completion of WebSockets data, but while the WebSockets connection doing duplex transfer there won't be any additional logging overhead (except by the application/service if it is designed to do so).
Typically, interactive applications that use AJAX either continuously poll or use some sort of long-poll mechanism. WebSockets is a much cleaner (and lower resource) way of doing a more event'd model where the server and client notify each other when they have something to report over the existing connection.
Most of the popular web servers in production have a pool of processes (or threads) for handling HTTP requests. As pressure increases the size of the pool will be increased because each process/thread handles one HTTP request at a time. Each additional process/thread uses more memory and creating new processes/threads is quite a bit more expensive than creating new socket connections (which those process/threads still have to do). Most of the popular WebSockets server frameworks are going the event'd route which tends to scale and perform better.
The primary benefit of WebSockets will be lower latency connections for interactive web applications. It will scale better and consume less server resources than HTTP AJAX/long-poll (assuming the application/server is designed properly), but IMO lower latency is the primary benefit of WebSockets because it will enable new classes of web applications that are not possible with the current overhead and latency of AJAX/long-poll.
Once the WebSockets standard becomes more finalized and has broader support, it will make sense to use it for most new interactive web applications that need to communicate frequently with the server. For existing interactive web applications it will really depend on how well the current AJAX/long-poll model is working. The effort to convert will be non-trivial so in many cases the cost just won't be worth the benefit.
Update:
Useful link: 600k concurrent websocket connections on AWS using Node.js
Just a clarification: the number of client connections that a server can support has nothing to do with ports in this scenario, since the server is [typically] only listening for WS/WSS connections on one single port. I think what the other commenters meant to refer to were file descriptors. You can set the maximum number of file descriptors quite high, but then you have to watch out for socket buffer sizes adding up for each open TCP/IP socket. Here's some additional info: https://serverfault.com/questions/48717/practical-maximum-open-file-descriptors-ulimit-n-for-a-high-volume-system
As for decreased latency via WS vs. HTTP, it's true since there's no more parsing of HTTP headers beyond the initial WS handshake. Plus, as more and more packets are successfully sent, the TCP congestion window widens, effectively reducing the RTT.
Any modern single server is able to server thousands of clients at once. Its HTTP server software has just to be is Event-Driven (IOCP) oriented (we are not in the old Apache one connection = one thread/process equation any more). Even the HTTP server built in Windows (http.sys) is IOCP oriented and very efficient (running in kernel mode). From this point of view, there won't be a lot of difference at scaling between WebSockets and regular HTTP connection. One TCP/IP connection uses a little resource (much less than a thread), and modern OS are optimized for handling a lot of concurrent connections: WebSockets and HTTP are just OSI 7 application layer protocols, inheriting from this TCP/IP specifications.
But, from experiment, I've seen two main problems with WebSockets:
They do not support CDN;
They have potential security issues.
So I would recommend the following, for any project:
Use WebSockets for client notifications only (with a fallback mechanism to long-polling - there are plenty of libraries around);
Use RESTful / JSON for all other data, using a CDN or proxies for cache.
In practice, full WebSockets applications do not scale well. Just use WebSockets for what they were designed to: push notifications from the server to the client.
About the potential problems of using WebSockets:
1. Consider using a CDN
Today (almost 4 years later), web scaling involves using Content Delivery Network (CDN) front ends, not only for static content (html,css,js) but also your (JSON) application data.
Of course, you won't put all your data on your CDN cache, but in practice, a lot of common content won't change often. I suspect that 80% of your REST resources may be cached... Even a one minute (or 30 seconds) CDN expiration timeout may be enough to give your central server a new live, and enhance the application responsiveness a lot, since CDN can be geographically tuned...
To my knowledge, there is no WebSockets support in CDN yet, and I suspect it would never be. WebSockets are statefull, whereas HTTP is stateless, so is much easily cached. In fact, to make WebSockets CDN-friendly, you may need to switch to a stateless RESTful approach... which would not be WebSockets any more.
2. Security issues
WebSockets have potential security issues, especially about DOS attacks. For illustration about new security vulnerabilities , see this set of slides and this webkit ticket.
WebSockets avoid any chance of packet inspection at OSI 7 application layer level, which comes to be pretty standard nowadays, in any business security. In fact, WebSockets makes the transmission obfuscated, so may be a major breach of security leak.
Think of it this way: what is cheaper, keeping an open connection, or opening a new connection for every request (with the negotiation overhead of doing so, remember it's TCP.)
Of course it depends on the application, but for long-term realtime connections (e.g. an AJAX chat) it's far better to keep the connection open.
The max number of connections will be capped by the max number of free ports for the sockets.
No it does not scale, gives tremendous work to intermediate routes switches. Then on the server side the page faults (you have to keep all those descriptors) are reaching high values, and the time to bring a resource into the work area increases. These are mostly JAVA written servers and it might be faster to hold on those gazilions of sockets then to destroy/create one.
When you run such a server on a machine any other process can't move anymore.
Problem:
I need to design a networking application that can handle network failures and switch to another network in case of failure.
Suppose I am using three ethernet connections and one wireless also . At a particular moment only one connection is being used.
How should I design my system so that it can switch to another network in case of failure.
I know this is very broad question but any pointers will help!
I'd typically make sure that there's routing on the network and run one (or more) routing protocol instances on the host. That way network failure is (mostly) transparent to the application, as the host OS takes care of sending packets the right way.
On the open-source side, I have good experiences with zebra and quagga, at least on linux machines.
Create a domain model for this, describing the network elements, the kind of failures you want to be able to detect and handle, and demonstrate that it works. Then plug in the network code.
have one class polling for the connection. If poll timeout fires switch the ethernet settings. For wireless, set the wifi settings to autoconnect and then just enable/disable the wificard.
(But I dont know how you switch the ethernet connection)
First thing I would do is look for APIs that will give me network disconnection events.
I'd also find a way to check the state of the network connections.
These would vary depending on the OS and the Language used so you might want to have this abstracted in your application.
Example:
RegisterDisconnectionEvent(DisconnectionHandler);
function DisconnectionHandler()
{
FindActiveNetworkConnection();
// do something else...
}
A primitive way to do it would be to look out for network disconnection events. Your sequence would be:
Register/poll for network connections status changes. Maintain a list of all active network connections.
Use the first available network connection (Alternately you could sort it based on interface bandwidths, and use the one with highest bandwidth).
When you detect a down connection, use the next active one.
However, if there are implications to the functionality of your application, based on which network connection you use, you are much better off, having either a routing protocol do the job for you, or have a tracking application within your application. This tracking application would track network paths (through various methods like ping, traceroute, etc) across all your available interfaces to see which one can reach the ultimate destination, and use the appropriate network interface.
Also, you could monitor your network interfaces for not just status changes, but also for input/output errors, and change your selection accordingly. This would help you use the most efficient network at any given point of time. But this would need to be balanced with the churn caused by switching a network connection.
If you control all of the involved hosts, Multipath TCP will probe all of your connections and automatically choose the one that works; if multiple connections are working, it will load balance across them.
If you don't control the endpoints, there's no choice but doing the probing in the application. Mosh is an example of an application that does that quite elegantly.
You didn't mention what your application does; perhaps it would be possible to redesign your protocol so that it uses all available connections simultaneously, the way BitTorrent does, and therefore doesn't care about some links being down at any given time?