I have a "gameserver.socket" and a "gameserver.service".
The service gets activated by systemd socket activation on first connection.
My issue is the following:
If I stop the "gameserver.service", it will get spawned immediately by "gameserver.socket".
Why this happens ?
Should not the "gameserver.socket" get back to "listening" mode, rather than "running" mode and when another connection is being made, then it should start the "gameserver.service" ?
your program needs to be compatible with socket activation
…
Note that the daemon software configured for socket activation with
socket units needs to be able to accept sockets from systemd, either
via systemd's native socket passing interface (see sd_listen_fds(3)
for details about the precise protocol used and the order in which the
file descriptors are passed) or via traditional inetd(8)-style socket
passing (i.e. sockets passed in via standard input and output, using
StandardInput=socket in the service file).
https://www.freedesktop.org/software/systemd/man/systemd.socket.html
Related
I am new to GNU Radio and Linux.
I want to send processed data out from gnu companion to a software/dashboard whose input is LAN/TCP/IP.
I am using RTL dongle and USRP and i have done GMSK demodulation successfully.Now want to send the demodulated data to a software for presentation and display developed by another team.The dashboard/software uses Ethernet data as input and has ip address and port as input parameters.
Currently i failed to send a random data via TCP sink and receive it via TCP source blocks on loopback address.
Please help me
Did you set the TCP Sink to "Server", and the Source Block to "Client"? Only the block that is set to "Client" needs to know the address, but both need to know the Port.
And is the port you use for your loopback test free, or could another program be using it?
Also, if the Nonblocking mode for the TCP blocks is off, the execution of the flowgraph is halted until a connection is established. I’m not sure but I think that could lead to problems if they are supposed to connect to each other in the same flowgraph.
Try using an external program (like netcat) for debugging instead. netcat will probably not display it correctly but it’ll tell you if any data at all is coming through.
Additionally, the TCP source and TCP sink blocks are deprecated and shouldn’t be used, use UDP or ZeroMQ for communicating with external programs instead, if possible.
I have put together an architecture that at high level is best described below
Five node docker swarm cluster
Have say 5 instances of my dockerized micro service running one copy on each of the swarm nodes
The service offers functionality via REST end points
One such functionality is downloads and they work perfectly, I wrote some code in Scala/Play framerwork, dockerized the service and deployed it.
I also know that since I use swarm , it internally does LB per request for me.
I have some questions on WebSocket and how load balancer does not ruin things during download.
I start a 5GB file download and it works. I am using HTTP stream or chunked I guess it does not matter. Now my question is once my REST end point for download is hit, the TCP connection remains open and since it is open until the server closes the connection, it is due to this that the swarm load balancing does not interfere? In short, each time a client requests a HTTP call, swarm load balances it but once the TCP socket is established as in case of specific download example, the request is served by one node as the connection is not re-stablished during the download process?
If a client opens a web socket, it will hit one of the nodes of swarm where the service is running and the websocket connection since it is open, the same service instance will push the notifications?
If for some reason the websocket dies, a new connection might be established by client but the request might end up on some other service instance and will remain like that until a new connection is again established?
Are above 3 points correct in my understanding? Is there some reading material/blogs I can find more on elaborating this?
Maybe using nginx like proxy LB, ip_hash mode
Specifies that a group should use a load balancing method where requests are distributed between servers based on client IP addresses. The first three octets of the client IPv4 address, or the entire IPv6 address, are used as a hashing key. The method ensures that requests from the same client will always be passed to the same server except when this server is unavailable. In the latter case client requests will be passed to another server. Most probably, it will always be the same server as well.
http://nginx.org/en/docs/http/ngx_http_upstream_module.html#ip_hash
I have 2 nodeMCU modules, which I want to connect to an MQTT broker and send some data every 5 seconds.
The topology I am trying to achieve is sth like [router]<==[nodeMCU#1]<==[nodeMCU#2]
It looks like [nodeMCU#1] is a wifi extender, but at work we are planning on using multiple nodeMCU's to use in a mesh-like way for an IoT application.
On both of them I flashed the latest (float) release that I downloaded from here https://github.com/nodemcu/nodemcu-firmware/releases/tag/0.9.6-dev_20150704 using nodeMCU-flasher.
For this project wrote 2 lua scripts and I have uploaded them to the modules using ESPlorer.
For the first module it connects in STATIONAP mode to my work wifi, and creates its own network with SSID nodeMCUwifi, with a basic password of 10 characters "1234567890". After it connects the script sends random values to an MQTT topic.
For the second module connects to nodeMCUwifi correctly, it is assigned an IP address, but it cannot connect to the MQTT broker.
When I try to connect to nodeMCUwifi using my smartphone (just to test the connection, I have no intention of using this system for heavy internet load, only MQTT messages) I get a message "authentication error occured" even though I have typed the password correctly, or (in rarer cases)it connects but disconnects immediately.
I would appreciate any ideas to resolve this issue. Thank you.
EDIT: At the AP configuration I added the auth parameter set to 3, I am pasting a part of my code below.
cfg.ssid="ESP8266_"..node.chipid();
cfg.pwd="1234567890"
cfg.auth=3
wifi.ap.config(cfg);
Now my laptop and my smartphone connect to the wifi created by the module, but still have no connectivity to the internet. I can ping the module, but I can't ping 8.8.8.8 or the MQTT broker IP or anything else.
As I understand, [nodeMCU#1] creates a wifi network named nodeMCUwifi. Then the others are trying to connect to nodeMCUwifi. As You stated:
Now my laptop and my smartphone connect to the wifi created by the module, but still have no connectivity to the internet. I can ping the module, but I can't ping 8.8.8.8 or the MQTT broker IP or anything else.
I assume your laptop and smartphone connects to the nodeMCUwifi network. Now you want this [nodeMCU#1] act like layer 2 switch or something like router(since SOFTAP creates its own ip network).
With all this information on hand, I can say that the purpose you are trying to achieve is not possible with esp. Since esp has not enough resources to act like switch or similar. Also (currently) there is no software implemented in esp to achieve that.
However; if only you want the system to transfer certain type of traffic (such as MQTT) over a certain protocol (such as UDP) it is possible to relay the messages like a mesh structure but this will work one-way only. In this configuration the nodes will act more like repeater but on upper layers of OSI. For this idea i cannot provide sample code but I will provide pseudo-code below:
Configuration
> Each node must be configured to build a chain structure. That means each SOFTAP node should have different SSID or TCP settings. For example:
router(192.168.0.0)<----[NODE#1(SOFTAP0)]<----[NODE#2(SOFTAP1)]<---...
...
...
...<----[NODE#n(STATION)]
> Each node must have a TARGET IP address according to setup. This means every node will send the MQTT message to that address.
> If a node is configured as a SOFTAP, this means this system is a TARGET and must listen to a specific port.
> If a SOFTAP node receives some data on the port that is listening to, it should send the data immediately (or buffering) to its TARGET node.
> As a result of this chaining operation the message, no matter what is the source, will reach to the end of the chain.
CODE : SOFTAP
...soft ap config...
listento.port: udp.965
on("receive"):
create.conn:TARGET
send(DATA_RECEIVED)
close.conn:TARGET
CODE : STATION
...station config...
...Do some logic...
data=gather.data()
create.conn:TARGET
send(data)
close.conn:TARGET
Is it allowed to have one process reading from and another process writing to a socket in Erlang?
I have tried it and it appears to work but I would like to know if it's foolproof.
As I understand it from the source code, a (gen_tcp, at least) socket send/recv boils down to an erlang:port_command for the send and an erlang:port_control for the recv on the socket port (see prim_inet.erl).
For port_command: "if the port is busy, the calling process will be suspended until the port is not busy anymore." The port_control is also a synchronous operation.
Correct me if I'm wrong, but it would appear to be completely safe to use multiple processes to read and write to a socket.
I am pretty sure I remember doing this without any problems.
Anyone of them can write, but it wouldn't make sense if all your processes could receive. It would overflow the mailboxes of all the ones not anticipating messages. You need to define only one Pid to receive packets, by default it's whatever Pid the socket was created in. You can set any Pid to control the socket by setting the controlling process.
I am a newbie in network related aspects. I have few basic questions related to tcp/ip protocol and network
If a network switch (in a LAN network) between two PC's running Client and server (that are communicating through async. sockets) is powered down. Can the client and server will be notified that the socket connection is no longer active. Client and server are running on Win XP OS and are coded using C#.
Does network topology play a role in case of half open connection between socket client and socket server. For e.g. Will a disconnect status of either one or both be notified to other end and does it depend on network topology.
Thanks in advance.
A network element such as a router/hub/switch does not activly cause anything anything to happen on the TCP layer if it goes down. The operating system might notice that the physical layer is down and error out all sockets bound on that network card if it's a network element directly connected to the PCs that breaks - this will vary among operating systems/network cards and other things. Other than that, in order to detect that the connection has been severed, you'll have to send something and rely on the TCP timeout mechanisms to error out. This can be done implicittly by enabling TCP Keepalives on the connection.
A disconnect on one side will only be noticed if those messages reach the other side, if the network topology changes or sometinhg breaks in the middle of the connection in such a way that messages no longer reach the other end, a disconnect won't be noticed. (NAT gateways are a big source of problems such as this, they might time out a TCP connection they're tracking and you'll never know the connection is no longer valid unless you try to write something (or enable TCP keepalives) to the connection). Note that most networking APIs require that you Read from the connection to discovver that a the other end has closed the connection - assuming those "close" messages actually reach your side.