I have never heard of the heartbeat until the heartbleed bug. I wonder what is the difference between this and a ping, and if there are other signals to manage the connection (also, which are not data packages).
Strictly speaking, ping refers to using an ICMP ECHO request to see if the destination computer is reachable. It tests the network, but not whether the target computer is able to usefully respond to any other particular service request (I've seen computers which were ping-able but which were functionally down; the OS kernel — which is what responds to pings — was up, but all user processes were dead).
However, the term has been extended to cover any sort of client-initiated check of whether the other end is up, often done inside the protocol of interest so that you can find out whether the target machine is able to do useful work.
With heartbeats, I've typically thought of them as being where the service regularly pushes the notification to somewhere else (as opposed to being prompted by a client). The idea is that the heartbeat monitor detects if it hasn't had a heartbeat signal for a while and applies “emergency CPR” (i.e., restarts the service) if that happens. It's similar to a watchdog timer in hardware.
I view a ping and a heartbeat as being complementary: one is for the client to learn whether the service is up, and the other is for the service provider to learn whether the service is up. (The provider could use a ping, and probably does via their Nagios setup, but a heartbeat monitors something slightly different — internal timers, in particular — and is pretty cheap to implement so there's no reason not to use one.)
Ironically, the Heartbleed bug was in what I'd consider to be a ping-ing mechanism. But it's called that because it's based on a (mis-)implementation of the SSL Heartbeat Extension. Terminology's all too often just there to be abused…
Related
Have found several SO Q&A's related to OpenShift's concept of application idling when there is no inbound traffic for 24 hours. Apart from the fact that there could be hacks to work around it, I was wondering, as to what is the effect since OpenShift claims that the application is brought back to full live state when an incoming request is encountered. In that case, apart from the fact that the HTTP request that causes application to go back from idle state to live/running state would run trifle slower, but is there any other inconvenience that I am missing here ?
In my experience, the first call after idling consistently fails. Subsequent calls do work then. This is probably due to a timeout, since it takes a while to spin up the gears. It may also depend on the time your application takes to activate, meaning this could be specific for my kind of application.
However I switched from the FREE plan to BRONZE a while ago and did not experience any problems since then.
I've been writing an extension that allows the user to issue voice commands to control their browser, and things were going great until I hit a catastrophic problem. It goes like this:
The speech recognition object is in continuous mode, and whenever the onerror: 'no-speech' or onend events fire, it restarts. This way, the extension is constantly waiting to accept input and reacts whenever a command is issued, even after 5 minutes of silence.
After a few days of of development, today I reached the point where I was testing it in practical use, and I found that after a little while (and with no change to anything on my part), my onend event started firing constantly. As in, looking at the console, I would see 18,000 requests being made in the space of three seconds, all being instantly denied, thus triggering onend and restarting the request.
I'm aware that it would be optimal to wait for sound before sending a request, or to have local speech recognition capabilities without the need for a remote server, but the present API does not allow that.
Are my suspicions correct? Am I getting request limited?
Are my suspicions correct? Am I getting request limited?
Yes
I'm aware that it would be optimal to wait for sound before sending a request, or to have local speech recognition capabilities without the need for a remote server, but the present API does not allow that.
To hide the IP source of your request you can use anonymizer networks like Tor, though it will not be fast.
It's naive to assume Google will spend resources to process all audio being recorded on your system. In your application development it is better to rely on API which provides at least some guarantees. It could be either commercial API or open source implementation like CMUSphinx.
With CMUSphinx, you can also properly implement command keyword detection and increase accuracy by specifying the grammar of the commands.
You could also use a Voice Activity Detection (VAD) algorithm to detect when a user is talking. This can be done by either setting a volume threshold or a frequency threshold (Human speech is usually less than 400hz for example). This way, you won't send useless requests to Google unless those conditions are meant. I would not recommend using Tor as this would significantly increase latency. CMUSphinx is probably the best local system option, but if still want to use a web-based service, I would recommend either using a Voice Activity Detection algorithm or finding a different web-based software.
Is there any utility like tcpdump in Linux for capturing the traffic which is going over RDMA channel? (Infiniband/RoCE/iWARP)
Old thread, but still:
As Roland pointed out, sniffing RDMA traffic is tricky, because once the endpoints did the initial handshake, traffic goes through network card (HCA) directly to the memory.
The only way to sniff this traffic w/o putting a dedicated HW sniffer on the wire is to have vendor-specific hooks in the network card, and a SW tool that uses these hooks.
If you have Mellanox HCAs, you can use the "ibdump" tool. This tool is also a part of Mellanox OFED package.
If you have other vendor's HW, you need to check with that vendor - you won't find any open-source packet sniffer for all RDMA-capable devices, sorry.
In general, no. One of the main characteristics of RDMA is that all the network processing is done on the adapter, without involving the CPU at all. Typically work requests are queued up directly from userspace to the adapter, without any system call. So there's nowhere for a sniffer to hook in to get traffic.
With that said, for Ethernet protocols, iWARP or IBoE (aka RoCE), you can hook up a system in the middle of a connection and set it up to do forwarding in software (eg the Linux bridge module) and then run tcpdump or wireshark to capture the RDMA traffic that passes through this system. Wireshark even has dissectors for iWARP and IBoE.
For native InfiniBand it is theoretically possible to build something similar (set up an adapter to capture and forward traffic) but as far as I know, no one has done even the needed firmware or driver work to do basic packet sniffing.
Chelsio's T4 device supports a packet trace feature allowing it to replicate ingress/egress offload packets to one of the device's NIC queues. Then you can use tcpdump or whatever on that ethX interface to see the RDMA or TOE packets.
Wireshark can be the one. But the problem is you need an observing server. Enabling the mirror feature, you should be able to receive the ROCE pocket at the observer.
A sure way to capture such traffic is to duplicate it into dedicated capture ports. Those ports might be additional ethernet/IB ports (of additional adapters) in your development machine or they may be located in an additional capture machine.
There are basically 2 ways how to duplicate the traffic:
Configure port-mirroring in your switch. Support for port mirroring is pretty common in managed Ethernet switches, even in cheap ones. This feature is also available in some Mellanox Infiniband switches. You can configure to mirror both directions of a port into another one, although this oversubscribes the receiver if the mirrored port receives and sends at line speed at the same time (full-duplex). In such a situation some frames can't be forwarded to the capture port then and are thus dropped. To avoid this limitation one needs to mirror each direction into a separate capture port.
Connect your network cable to a TAP (target access point) device that duplicates or splits the signal. With optical networking those TAPs are often constructed in a completely passive way and thus don't add much complexity and are relatively cheap to produce (examples). You need one TAP for each fiber, i.e. you always occupy 2 capture ports if you want to capture both directions. TAP devices are available for the fibers and connectors commonly used in Ethernet networks. If your Infiniband hardware uses the same then you should be able to use the same TAP devices there, as well. At least the passive ones.
Once the mirrored/tapped traffic arrive at your capture port(s), you can use standard capture tools such as tcpdump.
For Infiniband there is ibdump, however, depending on the Infiniband software you are using (open-source OFED vs. the proprietary Mellanox OFED) and the host channel adapter (HCA) you might be able to use tcpdump to capture Infiniband traffic, as well.
Is there a way to register code to be run when Flash is about to close (e.g., when the user closes the browser or when DOM manipulation causes the embedded player to be removed)?
In particular, I'd like for my application to send a closing packet to a remote service so the user's peers know that the user has no chance of coming back without having to wait for a timeout. I'm using URLLoader and URLRequest to maintain a BOSH connection, so I welcome solutions applicable to this specific case. However, if there are NetConnection-specific solutions, I'm sure I can learn from them too.
I'm happy to accept that this callback won't be run on a kill -9 but it would be nice to have the more graceful exit paths allow for some code execution.
It seems like the better solution would be to do this via the server side no? The server should be able to detect the disconnection, where you could then invalidate the session.
However, you could go with a client/socket based solution, albeit much more overhead. Using FMS or some other rtm real time server you could dispatch events to your web server that a connection has dropped, (though you might have issues in the case of low network connectivity, or an internet drop). I would suggest going against this though, as in my experience, FMS sucks :)
Is setting extremely low timeouts not a possibility? (i.e. < 10 seconds)
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?