The Micrometer library has a JettyConnectionMetrics class which produces these metrics (among others):
# HELP jetty_connections_bytes_in_bytes Bytes received by tracked connections
# TYPE jetty_connections_bytes_in_bytes summary
jetty_connections_bytes_in_bytes_count 125.0
jetty_connections_bytes_in_bytes_sum 186955.0
# HELP jetty_connections_bytes_in_bytes_max Bytes received by tracked connections
# TYPE jetty_connections_bytes_in_bytes_max gauge
jetty_connections_bytes_in_bytes_max 1681.0
What does this actually count? What does tracked mean here?
If I add it to our (only one) connector will it contain every bytes received by the TCP connection?
I am right that it is updated only on connection close which could delay data when there is a HAProxy between real clients and Jetty (with keep-alive connections)?
What does this actually count?
According to the code of this class, it measure the following points:
Messages received by tracked connections
Messages sent by tracked connections
Bytes received by tracked connections
Bytes sent by tracked connections
The maximum number of observed connections over a rolling 2-minute interval
The current number of open Jetty connections
What does tracked mean here?
Because JettyConnectionMetrics is Jetty's Connection.Listener, when registered into a Connector, it'll track all open and close events, i.e. whenever an I/O event occurs on that connector.
If I add it to our (only one) connector will it contain every bytes received by the TCP connection?
Yes, if you are using ServerConnector, that is the primary connector for the Jetty server over TCP/IP.
I am right that it is updated only on connection close which could delay data when there is a HAProxy between real clients and Jetty (with keep-alive connections)?
Yes, you're right, that is updated only when a connection closes. Depending how is this important for your metrics, you may consider disabling keep-alive connections and require always that connections get closed (make sure you understand the trade-offs of this change).
Related
I have made a client and a server using Indy TIdTCPClient and TIdTCPServer in C++Builder 11 Alexandria.
I can start the server and connect the client to it correctly, but if I set the server MaxConnections to a value N and I try to connect to it with the N+1 client, the connection does not fail, apparently.
For example: I set MaxConnections=1 in the server, the first client connects to it and the server OnConnect event is raised, while in the client OnStatus event I get two messages:
message 1: Connecting to 10.0.0.16.
message 2: Connected.
I try to connect the second client: the server OnConnect event is NOT raised (and this is what I expect) but in the client OnStatus event I get the same two messages (and this is not what I expect):
message 1: Connecting to 10.0.0.16.
message 2: Connected.
Then, the first client can exchange data with the server, and the second client can't (this seems right).
I don't understand why the second client connection does not fail explicitly, am I doing something wrong?
You are not doing anything wrong. This is normal behavior for TIdTCPServer.
There is no cross-platform socket API at the OS level 1 to limit the number of active/accepted connections on a TCP server socket, only to limit the number of pending connections in the server's backlog. That limit is handled by the TIdTCPServer::ListenQueue property, which is 15 by default (but this is more of a suggestion than a hard limit, the underlying socket stack can override this, if it wants to).
As such, the TIdTCPServer::MaxConnections property is implemented by simply accepting any client from the backlog that attempts to connect, and then immediately disconnects that client if the MaxConnections limit is exceeded.
So, if you try to connect more clients to TIdTCPServer than MaxConnections allows, those extra clients will not see any failure in connecting (unless the backlog fills up), but the server will not fire the OnConnect event for them. From the clients' perspectives, they actually did connect successfully, they were fully accepted by the server's underlying socket stack (the TCP 3way handshake is complete). However, they simply will not process the disconnect until they try to actually communicate with the server, then they will detect the disconnect, usually in the form of an EIdConnClosedGracefully exception (but that is not guaranteed).
1: on Windows only, there is a WSAAccept() function which has a callback that can reject pending connections before they leave the backlog queue. But Indy does not make use of this callback at this time.
Different TCP stacks exhibit different behavior. Your description is consistent with a TCP stack that simply ignores SYNs to a socket that has reached the maximum configured limit of pending and/or accepted connections: the SYN packet is simply dropped on the floor and not acknowledged.
The nature of TCP is that it's supposed to handle network drops. The sender does not immediately bail out, but will keep trying to connect, for some period of time. This part is consistent with all TCP implementations.
If you want your client to quickly fail a connection that does not get established within some set period of time you'll need to implement a manual timeout yourself.
I'm using Jetty 9.2.24 as a WebSocket server. I want to detect half-open connections, so that no more messages are sent over this connection and buffered instead.
I know PING/PONG frames are used for this, so I tried sending PINGs periodically and set a low maxIdleTimeout. I modified my client to NOT return a PONG to see if Jetty would regard this as a failed connection since the RFC-6455 spec dictates that the remote endpoint MUST respond with a PONG. Apparently Jetty does not detect missing PONGs or I am doing something wrong.
What is the best way to continue. Should I implement the PING/PONG timeouts myself by explicitly receiving all PONG messages and detect a timeout? I would think this would be responsibility of the underlying websocket managing framework.
Note that Jetty 9.2.x is EOL (End of Life) you should consider upgrading.
Setting Max Idle Timeout and then causing the connection to not be idle by sending ping/pong isn't ideal.
The spec says that when you receive a PING you must send a PONG, and Jetty indeed does that.
It does not say that receiving a PONG, or not receiving a PONG, or receiving an unsolicited PONG has any meaning or behavior on it like you think it should.
Jetty 9.4 websocket will only keep a half-open connection open long enough to complete the current message (no matter how many frames it takes) then respond to the CLOSE frame it received (that caused the half-open connection). So half-open is only for the duration of the active message, then CLOSED. If no message is active, then the CLOSE happens immediately.
On Jetty 9.4 you can also add a WebSocketFrameListener and respond accordingly based on the frames received (eg: make the server end the conversation immediately, either via a CLOSE frame, or harsh disconnect)
I am doing a TCP client - server simulation. In the simulation, I have created 2 clients and 2 servers. And I have programmed that read requests will go to server 1 and write requests will go to server 2. Thus, the client will always renew it's socket and make a new connection to the servers.
However, after the client has made 66561 times of connections to the server, instead of sending request packets, it will just simply send some empty ACK packets.
I expected both the clients to be able to send up to millions of requests, but currently, both the clients are only able to send up to 13k requests. Can anyone give me tips or advices?
Nagle's algorithm
Solutions:
Do not use small package in your app protocol
Use socket option TCP_NODELAY on both side client/server
Sounds like most previously created connections are still taking the resource (not released from system). From the information you give,
However, after the client has made 66561 times of connections to the server, instead of sending request packets, it will just simply send some empty ACK packets.
Looks like about 1000+ connections are released. Probably because of the 2msl time is due. If this is the case, suggest you explicitly release a connect before you create a new one.
Copy and paste your C/S part code would help the analyse.
I need a little help if someone's got a minute.
I've written a web server using IO completion ports, but I am having some trouble sending out large files. Web pages seem to load fine, but during large file transfers, WSASend() fails after a few minutes with error "The specified network name is no longer available."
Right now, my server just closes the associated connection when any overlapped operation fails. Is this the right thing to do? or should I retry failed overlapped operations a few times before I close the socket? I am using tcp/stream sockets.
(fixed) I am also receiving what seems like random 0 byte packets from WSARecv. I am not sure what to make of this, or if the problem is related.(/fixed)
Thanks for any help
edit: now that the server properly handles connections, and has a much more comprehensive log, it seems like Len is right. The client is closing the connection for some reason.
The log:
Initializing Windows Sockets...
Forwarding port 80...
Starting server...
Waiting for incoming connections...
Socket 1128: Client connected.
Socket 1128: Request received
Socket 1128: Sent response
Socket 1128: Error 64: SendChunk() failed. //WSASend()
Socket 1128: Closing connection - GetQueueCompletionStatus == FALSE
so the question is now, why would the client close the connection? It takes anywhere from 2-5 minutes to happen. I have decreased the buffer size to 4098 bytes per send, and only send the next chunk when the first has completed.
Thanks again for any ideas on this.
p.s. I even just implemented a retry function so that it will retry a failed overlapped IO operation five times before giving up....still no luck =(
A zero length packet returned from recv indicates client on the other end has closed the connection.
Which answers why your subsequent send to the client failed.
http://www.opengroup.org/onlinepubs/009695399/functions/recv.html
If no messages are available to be
received and the peer has performed an
orderly shutdown, recv() shall return
0.
Are you doing anything to impose some form of flow control on your data transmission?
If not then you are probably using up resources which is causing the send to fail.
For example, if you are simply issuing LOTS of WSASend() calls one after the other rather than pacing them based on when they complete then each one will use system resources (non-paged pool and/or lock pages which go towards the 'locked pages limit'). You'll then likely eventually fail with ENOBUFS or similar errors.
What you need to do is build a flow control system that works off of the send completions so that you only ever have a known number of sends outstanding at a time.
See these questions for more detail:
Implement a good performing "to-send" queue with TCP
Limiting TCP sends with a "to-be-sent" queue and other design issues
Finally figured it out.
from Rogers Internet Terms of Service:
Without limitation, you may not use (or allow anyone else to use) our Services to:
(xvi) operate a server in connection with the Services, including, without limitation, >mail, news, file, gopher, telnet, chat, Web, or host configuration servers, multimedia >streamers or multi-user interactive forums;
how lame is that? O_o
good news: server works fine =)
edit- called Rogers. They verified that they are cutting me off, and told me that I need a business account to run a web server.
Hey gang. I have just written a client and server in C++ using sys/socket. I need to handle a situation where the client is still active but the server is down. One suggested way to do this is to use a heartbeat to periodically assert connectivity. And if there is none to try to reconnect every X seconds for Y period of time, and then to time out.
Is this "heartbeat" the best way to check for connectivity?
The socket I am using might have information on it, is there a way to check that there is a connection without messing with the buffer?
If you're using TCP sockets over an IP network, you can use the TCP protocol's keepalive feature, which will periodically check the socket to make sure the other end is still there. (This also has the advantage of keeping the forwarding record for your socket valid in any NAT routers between your client and your server.)
Here's a TCP keepalive overview which outlines some of the reasons you might want to use TCP keepalive; this Linux-specific HOWTO describes how to configure your socket to use TCP keepalive at runtime.
It looks like you can enable TCP keepalive in Windows sockets by setting SIO_KEEPALIVE_VALS using the WSAIoctl() function.
If you're using UDP sockets over IP you'll need to build your own heartbeat into your protocol.
Yes, this heartbeat is the best way. You'll have to build it into the protocol the server and client use to communicate.
The simplest solution is to have the client send data periodically and the server close the connection if it hasn't received any data from the client in a particular period of time. This works perfectly for query/response protocols where the client sends queries and the server sends responses.
For example, you can use the following scheme:
The server responds to every query. If the server does not receive a query for two minutes, it closes the connection.
The client sends queries and keeps the connection open after each one.
If the client has not send a query for one minute, it sends an "are you there" query. The server responds with "yes I am". This resets the server's two minutes timer and confirms to the client that the connection is still available.
It may be simpler to just have the client close the connection if it hasn't needed to send a query for the past minute. Since all operations are initiated by the client, it can always just open a new connection if it needs to perform a new operation. That reduces it to just this:
The server closes the connection if it hasn't received a query in two minutes.
The client closes the connection if it hasn't needed to send a query in one minute.
However, this doesn't assure the client that the server is present and ready to accept a query at all times. If you need this capability, you will have to implement an "are you there" "yes I am" query/response into your protocol.
If the other side has gone away (i.e. the process has died, the machine has gone down, etc.), attempting to receive data from the socket should result in an error. However if the other side is merely hung, the socket will remain open. In this case, having a heartbeat is useful. Make sure that whatever protocol you are using (on top of TCP) supports some kind of "do-nothing" request or packet - each side can use this to keep track of the last time they received something from the other side, and can then close the connection if too much time elapses between packets.
Note that this is assuming you're using TCP/IP. If you're using UDP, then that's a whole other kettle of fish, since it's connectionless.
Ok, I don't know what your program does or anything, so maybe this isn't feasible, but I suggest that you avoid trying to always keep the socket open. It should only be open when you are using it, and should be closed when you are not.
If you are between reads and writes waiting on user input, close the socket. Design your client/server protocol (assuming you're doing this by hand and not using any standard protocols like http and/or SOAP) to handle this.
Sockets will error if the connection is dropped; write your program such that you don't lose any information in the case of such an error during a write to the socket and that you don't gain any information in the case of an error during a read from the socket. Transactionality and atomicity should be rolled into your client/server protocol (again, assuming you're designing it yourself).
maybe this will help you, TCP Keepalive HOWTO
or this SO_SOCKET