I am writing a Golang ssh/sftp client which connects to a sftp server with a slowness in connecting and writing files, using golang.org/x/crypto/ssh package. I need to set Connection timeout and SO timeout (as we do in Java JSCH library).
First to achieve Connection timeout I was using ssh.ClientConfig.Timeout, but only worked for nanosecond and microsecond values, not for milliseconds and above, where I needed to set 5 seconds. According to the API doc also I assume ssh.ClientConfig.Timeout is used only for TCP socket connection creation and ssh handshake is not included there.
So then I tried net.Conn.SetDeadline() and it was for end-to-end connection creation + writing file + connection closing. Since this is also not fine, tried net.Conn.SetWriteDeadline() which looks like SO timeout (applied in TCP packet level) but timeout error is not appeared just after the duration elasped, instead comes out after the server's late reply or subsequent write operation starts.
So can someone please show the correct way of setting Connection timeout and SO timeout in Golang ssh package or tell whether this is supported or not?
Related
The database i'm integrated is configured as if a connection is idle(not being used for a while), then connection is dropped. Since im using spring batch in persistent configuration, there is always an active database connection on running threads.
One of my spring batch job is dependent to data from external web service which takes long time to execute. Thats why i already lose the database connection when i get the result.
I tried to use taskscheduler to register a heartbeat query(select 1 from dual) before the web request occurs, which executes the queryevery 5 minutes to keep the connection alive but even if the query executes periodically, i guess it executes the query on a seperate connecyion since it runs on another thread.
Does anyone have an alternative suggestion to keep the connection alive while on locked thread?
I use JPA's EntityManager for the haertbeat query
If you use Spring then you also use HikariCP. The recent JDBC standard defines method isValid() so you do not have to call SQL to check whether Connection is alive.
More over there is one more mechanism you can use. It is called TCP keepalive.
If you insert stanza ENABLE=BROKEN into your JDBC url Oracle JDBC drivers will enable TCP Keepalive feature on a TCP connection
jdbc:oracle:thin:#(DESCRIPTION=(ENABLE=BROKEN)(ADDRESS=(PROTOCOL=tcp)(PORT=1521)(HOST=myhost))(CONNECT_DATA=(SERVICE_NAME=orcl)))
Then it will be Linux kernel who will be sending keepalive probes over TCP connection even if your thread is blocked.
Beware: The delay for 1st probe and frequency is determined by Linux kernel parameters.
# cat /proc/sys/net/ipv4/tcp_keepalive_time
7200
# cat /proc/sys/net/ipv4/tcp_keepalive_intvl
75
# cat /proc/sys/net/ipv4/tcp_keepalive_probes
9
By default the 1st keep alive probe (TCP window carying 0 bytes) is sent after 2 hours.
While Cisco/Juniper usually cut off TCP connection after one hour.
So I read this article https://www.baeldung.com/httpclient-timeout and it says that connection timeout adds to its own penalty if the underlying service's DNS that httpclient tries to connect to has multiple IPs configured to it.
So if I have a connection timeout set to 100ms and the called service DNS has 5 IPs mapped to it then, I am looking at a max connection timeout of 500ms assuming what works is the last IP.
Is there a way to have a cap on this connection timeout regardless what the underlying service topology is as being a client, I will always be agnostic to it.
As far as I understood, you don't have a code-wise case to run in 5 or more IPs situation rather curiosity. So here my experience :
Since you're using RestTemplate which by default uses SimpleClientHttpRequestFactory.
And as the definition of connection time out goes :
The connection timeout is the timeout in making the initial
connection; i.e. completing the TCP connection handshake and getting
connected to the requested Server.
So, as far as theory goes :
Regardless of the underlying service topology, RestTemplate will try to make connection as per the connection timeout value.
And in order to figure out the almost exact timeout in your case, you must run some latency test, print the time differences which restTemplate is taking to get 200 OK.
Also, SimpleClientHttpRequestFactory internally uses HttpURLConnection which has default timeout of infinite (0/-1).
Yes, it has also been observed in rare cases, the connection keeps trying unless Thread.interrupt() explicitly being called to end.
Thus it becomes vital to describe your read-time-out and connection-time-out values and in this way you cap your connection to the limits you defined.
Hope this helps.
I have written a oracle client program using OCI library.
client send a request to server and hung because server crashed and not intimated to client.
How can i find server status from client side(using OCI API).?
Thanks
I think Oracle db module for Asterisk had a nice DCD(dead connection detection) implemented. There are various approaches(server side, client side).
In your case the easiest way would be to use TCP keepalive. Use enable=broken directive in tnsnames.ora.
Purpose
The keepalive feature on the supported TCP transports can be enabled
for a net service client by embedding (ENABLE=BROKEN) under the
DESCRIPTION parameter in the connect string. Keepalive allows the
caller to detect a dead remote server, although typically it will take
2 hours or more to notice. Operating system TCP configurables, which
vary by platform, define the actual keepalive timing details.
net_service_name=
(DESCRIPTION=
(enable=broken)
(ADDRESS=(PROTOCOL=tcp)(HOST=sales1-svr)(PORT=1521))
(ADDRESS=(PROTOCOL=tcp)(HOST=sales2-svr)(PORT=1521)))
(CONNECT_DATA=(SERVICE_NAME=sales.us.example.com))
Just beware you will also need root privileges. With default setting Linux kernel starts sending keepalive packets after 2 hours of inactivity. So you also have to change tcp_keepalive_time and tcp_keepalive_intvl in /etc/sysctl.conf. This is global server side settings and Oracle can not yet set keepalive interval for a single TCP connection.
One more comment: I recall there is some function called OCIPing.
This one can be used for testing too. But I'm not sure how to distinguish long running queries from dead server situation.
A few weeks ago I wrote a small program which created a socket to an apache webserver and made a request.
Back then I did not know that this web server had a KeepAliveTimeout of 5 seconds.
After my first request I waited 1 minute. After this I wanted to reuse my first socket for another webserver request, but got an error.
From Beej's Guide to Network Programming I learned that if recv returns 0, then the other side has closed its connection:
Wait! recv() can return 0. This can mean only one thing: the remote side has closed
the connection on you! A return value of 0 is recv()'s way of letting you know this
has occurred.
My questions are now:
What does Apache send when the KeepAliveTimeout is over - a FIN or a RST packet?
I know that using a TCP connection for 2 unrelated HTTP requests like in this scenario might
not be the best thing. But in order to understand TCP more the next question is:
After my first successful http request, and before sending the next HTTP request over the same socket, would there be somehow a possibility to get informed about this keepalivetimeout TCPsocket termination of the server other than receiving 0 from the next recv() call?
It will send a FIN. If you write a request to the server after that, send() will return -1 with errno/WSAGetLastError() = ECONNRESET.
would there be somehow a possibility to get informed about this keepalivetimeout tcp socket termination of the server
Yes, by reading the proper response header parameter, namely Keep-Alive: timeout=delta-seconds:
'timeout' Parameter
A host sets the value of the timeout parameter to the time that the host will allows an idle connection to remain open before it is closed. A connection is idle if no data is sent or received by a host.
The value of the timeout parameter is a single integer in seconds.
A host MAY keep an idle connection open for longer than the time that it indicates, but it SHOULD attempt to retain a connection for at least as long as indicated.
As you can see, it's up to the host to decide. Given it only SHOULD try to keep the connection open as long as promised, but it isn't required that it does in order to conform to the spec, so the server might decide to close and reuse the connection to serve another pending client.
When the Oracle 10 databases are up and running fine, OCILogon2() will connect immediately. When the databases are turned off or inaccessible due to network issues - it will fail immediately.
However when our DBAs go into emergency maintenance and block incomming connections, it can take 5 to 10 minutes to timeout.
This is problematic for me since I've found that OCILogin2 isn't thread safe and we can only use it serially - and I connect to quite a few Oracle DBs. 3 blocked servers X 5-10 minutes = 15 to 30 minutes of lockup time
Does anyone know how to set the OCILogon2 connection timeout?
Thanks.
I'm currenty playing with OCI and it seems to me that it's impossible.
The only way I can think of is to use non-blocking mode. You'll need OCIServerAttach() and OCISessionBegin() instead of OCILogon() in this case. But when I tried this, OCISessionBegin() constantly returns OCI_ERROR with the following error code:
ORA-03123 operation would block
Cause: The attempted operation cannot complete now.
Action: Retry the operation later.
It looks strange and I don't yet know how to deal with it.
Possible workaround is to run your logon in another process, which you can kill after timeout...
We think we found the right file setting - but it's one of those problems where we have to wait until something rare and horrible occurs before we can verify it :-/
[sqlnet.ora]
SQLNET.OUTBOUND_CONNECT_TIMEOUT=60
From the Oracle docs..
http://download.oracle.com/docs/cd/B28359_01/network.111/b28317/sqlnet.htm#BIIFGFHI
5.2.35 SQLNET.OUTBOUND_ CONNECT _TIMEOUT
Purpose
Use the SQLNET.OUTBOUND_ CONNECT _TIMEOUT parameter to specify the time, in seconds, for a client to establish an Oracle Net connection to the database instance.
If an Oracle Net connection is not established in the time specified, the connect attempt is terminated. The client receives an ORA-12170: TNS:Connect timeout occurred error.
The outbound connect timeout interval is a superset of the TCP connect timeout interval, which specifies a limit on the time taken to establish a TCP connection. Additionally, the outbound connect timeout interval includes the time taken to be connected to an Oracle instance providing the requested service.
Without this parameter, a client connection request to the database server may block for the default TCP connect timeout duration (approximately 8 minutes on Linux) when the database server host system is unreachable.
The outbound connect timeout interval is only applicable for TCP, TCP with SSL, and IPC transport connections.
Default
None
Example
SQLNET.OUTBOUND_ CONNECT _TIMEOUT=10