I've customers with Android mobiles with my app which forwards selective SMS to a Nodejs based Websocket server on Ubuntu 16.
I've two set of customers and another similar Ubuntu 14 with similar app and Nodejs server.
It has been working fine without any problem since 1.6 years.
But since 4 days this Ubuntu 16 version is causing some connection delay of some 5-10 seconds. I've not made any server configuration changes. In fact I've even increased open file limit to some 25000. Still the delay is not going away.
I checked on new Ubuntu 20, with same app and Nodejs code, no problems.
I'm sure that this delay of Websocket opening/delivery is due to server issue(by Linode)
What could be the problem in server configuration of Ubuntu 16 changed automatically?
dmesg shows:
[35228.191860] [UFW BLOCK] IN=eth0 OUT= MAC=f2:3c:92:29:94:db:a2:3e:34:00:2c:88:86:dd SRC=2402:8100:2858:25c4:5e8e:548a:75c4:33ea DST=2400:8904:0000:0000:f03c:92ff:fe29:94db LEN=80 TC=136 HOPLIMIT=239 FLOWLBL=887511 PROTO=TCP SPT=42688 DPT=8000 WINDOW=65535 RES=0x00 SYN URGP=0
[35248.292921] [UFW BLOCK] IN=eth0 OUT= MAC=f2:3c:92:29:94:db:a2:3e:34:00:2c:88:86:dd SRC=2401:4900:27ea:549d:0000:0067:9b6e:9101 DST=2400:8904:0000:0000:f03c:92ff:fe29:94db LEN=80 TC=104 HOPLIMIT=239 FLOWLBL=100574 PROTO=TCP SPT=47360 DPT=8000 WINDOW=65535 RES=0x00 SYN URGP=0
[35268.212187] [UFW BLOCK] IN=eth0 OUT= MAC=f2:3c:92:29:94:db:a2:3e:34:00:2c:88:86:dd SRC=2409:4070:2e08:cca8:921e:b0f7:b6bd:bfb4 DST=2400:8904:0000:0000:f03c:92ff:fe29:94db LEN=80 TC=40 HOPLIMIT=239 FLOWLBL=117961 PROTO=TCP SPT=38748 DPT=8000 WINDOW=65535 RES=0x00 SYN URGP=0
[35288.229850] [UFW BLOCK] IN=eth0 OUT= MAC=f2:3c:92:29:94:db:a2:3e:34:00:2c:88:86:dd SRC=2409:4070:2e08:cca8:921e:b0f7:b6bd:bfb4 DST=2400:8904:0000:0000:f03c:92ff:fe29:94db LEN=80 TC=40 HOPLIMIT=239 FLOWLBL=1048351 PROTO=TCP SPT=39068 DPT=8000 WINDOW=65535 RES=0x00 SYN URGP=0
[35308.192073] [UFW BLOCK] IN=eth0 OUT= MAC=f2:3c:92:29:94:db:a2:3e:34:00:2c:88:86:dd SRC=2401:4900:27d5:0b27:0000:0030:f685:db01 DST=2400:8904:0000:0000:f03c:92ff:fe29:94db LEN=80 TC=104 HOPLIMIT=48 FLOWLBL=0 PROTO=TCP SPT=41325 DPT=8000 WINDOW=65535 RES=0x00 SYN URGP=0
[35328.234821] [UFW BLOCK] IN=eth0 OUT= MAC=f2:3c:92:29:94:db:a2:3e:34:00:2c:88:86:dd SRC=2409:4070:2e08:cca8:921e:b0f7:b6bd:bfb4 DST=2400:8904:0000:0000:f03c:92ff:fe29:94db LEN=80 TC=40 HOPLIMIT=239 FLOWLBL=468322 PROTO=TCP SPT=39628 DPT=8000 WINDOW=65535 RES=0x00 SYN URGP=0
syslog is full with similar messages as above:
Feb 18 14:27:01 host kernel: [15186.889213] [UFW BLOCK] IN=eth0 OUT= MAC=f2:3c:92:29:94:db:1a:12:1c:98:45:62:86:dd SRC=2401:4900:482f:ec54:3d4e:8b0f:f262:949c DST=2400:8904:0000:0000:f03c:92ff:fe29:94db LEN=80 TC=104 HOPLIMIT=240 FLOWLBL=510821 PROTO=TCP SPT=45727 DPT=8000 WINDOW=65535 RES=0x00 SYN URGP=0
Feb 18 14:27:21 host kernel: [15206.851132] [UFW BLOCK] IN=eth0 OUT= MAC=f2:3c:92:29:94:db:1a:12:1c:98:45:62:86:dd SRC=2409:4070:221c:5c10:0000:0000:0976:70b1 DST=2400:8904:0000:0000:f03c:92ff:fe29:94db LEN=80 TC=40 HOPLIMIT=48 FLOWLBL=513590 PROTO=TCP SPT=50402 DPT=8000 WINDOW=65535 RES=0x00 SYN URGP=0
