inno-devops-labs · Long1Tail · Jun 5, 2026 · Jun 7, 2026 · Jun 7, 2026 · Jun 7, 2026
diff --git a/.github/pull_request_template.md b/.github/pull_request_template.md
@@ -0,0 +1,13 @@
+## Goal
+<!-- What does this PR accomplish? 1 sentence. -->
+
+## Changes
+- 
+
+## Testing
+<!-- How did you verify it? -->
+
+## Checklist
+- [ ] Title is a clear sentence (≤ 70 chars)
+- [ ] Commits are signed (`git log --show-signature`)
+- [ ] `submissions/labN.md` updated
diff --git a/submissions/lab4.md b/submissions/lab4.md
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+# Lab 4 submission
+
+### TCP Handshake (SYN -> SYN,ACK -> ACK):
+
+```
+22:33:46.570258 IP6 ::1.52782 > ::1.8080: Flags [S], seq 284201099, win 65476, options [mss 65476,sackOK,TS val 2276206117 ecr 0,nop,wscale 10], length 0
+`....(.@.................................................0.........
+..&%.......
+
+22:33:46.570285 IP6 ::1.8080 > ::1.52782: Flags [S.], seq 2388979400, ack 284201100, win 65464, options [mss 65476,sackOK,TS val 2618398189 ecr 2276206117,nop,wscale 10], length 0
+`
+.'.(.@.....................................d...........0.........
+......&%...
+
+22:33:46.570305 IP6 ::1.52782 > ::1.8080: Flags [.], ack 1, win 64, options [nop,nop,TS val 2276206117 ecr 2618398189], length 0
+`.... .@.........................................d.....@.(.....
+..&%....
+```
+
+### HTTP Request + (HTTP POST -> Server ACK):
+
+```
+22:33:46.570448 IP6 ::1.52782 > ::1.8080: Flags [P.], seq 1:176, ack 1, win 64, options [nop,nop,TS val 2276206117 ecr 2618398189], length 175: HTTP: POST /notes HTTP/1.1
+`......@.........................................d.....@.......
+..&%....POST /notes HTTP/1.1
+Host: localhost:8080
+User-Agent: curl/8.20.0
+Accept: */*
+Content-Type: application/json
+Content-Length: 39
+
+{"title":"trace me","body":"in flight"}
+22:33:46.570462 IP6 ::1.8080 > ::1.52782: Flags [.], ack 176, win 64, options [nop,nop,TS val 2618398189 ecr 2276206117], length 0
+`
+.'. .@.....................................d.....;...@.(.....
+......&%
+22:33:46.570917 IP6 ::1.8080 > ::1.52782: Flags [P.], seq 1:207, ack 176, win 64, options [nop,nop,TS val 2618398190 ecr 2276206117], length 206: HTTP: HTTP/1.1 201 Created
+`
+.'...@.....................................d.....;...@.......
+......&%HTTP/1.1 201 Created
+Content-Type: application/json
+Date: Tue, 16 Jun 2026 19:33:46 GMT
+Content-Length: 93
+
+{"id":7,"title":"trace me","body":"in flight","created_at":"2026-06-16T19:33:46.570565538Z"}
+```
+
+### Connection close (FIN->FIN,ACK->ACK)
+```
+22:33:46.570930 IP6 ::1.52782 > ::1.8080: Flags [.], ack 207, win 64, options [nop,nop,TS val 2276206118 ecr 2618398190], length 0
+`.... .@.......................................;.d.....@.(.....
+..&&....
+22:33:46.571020 IP6 ::1.52782 > ::1.8080: Flags [F.], seq 176, ack 207, win 64, options [nop,nop,TS val 2276206118 ecr 2618398190], length 0
+`.... .@.......................................;.d.....@.(.....
+..&&....
+22:33:46.571050 IP6 ::1.8080 > ::1.52782: Flags [F.], seq 207, ack 177, win 64, options [nop,nop,TS val 2618398190 ecr 2276206118], length 0
+`
+.'. .@.....................................d.....<...@.(.....
+......&&
+22:33:46.571067 IP6 ::1.52782 > ::1.8080: Flags [.], ack 208, win 64, options [nop,nop,TS val 2276206118 ecr 2618398190], length 0
+`.... .@.......................................<.d.....@.(.....
+..&&....
+```
+
+## Debug commands
+
+```
+$ ss -tlnp   | grep :8080
+LISTEN 0      4096               *:8080             *:*    users:(("quicknotes",pid=12601,fd=3))
+```
+
+```
+$ ip route show  
+0.0.0.0/1 dev amn0 metric 1 
+default via 192.168.0.1 dev eno1 proto dhcp src 192.168.0.100 metric 1002 
+default via 10.91.80.1 dev wlan0 proto dhcp src 10.91.86.43 metric 3004 
+10.91.80.0/20 dev wlan0 proto dhcp scope link src 10.91.86.43 metric 3004 
+31.172.78.99 via 192.168.0.1 dev eno1 
+128.0.0.0/1 dev amn0 metric 1 
+172.17.0.0/16 dev docker0 proto kernel scope link src 172.17.0.1 linkdown 
+172.18.0.0/16 dev br-bcc608ebbdf4 proto kernel scope link src 172.18.0.1 linkdown 
+172.19.0.0/16 dev br-2f04123ec594 proto kernel scope link src 172.19.0.1 linkdown 
+172.20.0.0/16 dev br-204ddeb962fd proto kernel scope link src 172.20.0.1 linkdown 
+172.21.0.0/16 dev br-507a46b4b473 proto kernel scope link src 172.21.0.1 linkdown 
+185.27.192.209 via 192.168.0.1 dev eno1 
+188.130.155.215 via 192.168.0.1 dev eno1 
+188.130.155.243 via 192.168.0.1 dev eno1 
+188.130.155.250 via 192.168.0.1 dev eno1 
+192.168.0.0/24 dev eno1 proto dhcp scope link src 192.168.0.100 metric 1002 
+```
+
+```
+$ mtr -rwc 5 localhost 
+Start: 2026-06-16T22:42:19+0300
+HOST: Long1Tail Loss%   Snt   Last   Avg  Best  Wrst StDev
+  1.|-- localhost  0.0%     5    0.1   0.1   0.1   0.1   0.0
+```
+
+```
+$ dig +short example.com @1.1.1.1
+172.66.147.243
+104.20.23.154
+```
+
+```
+$ journalctl --user -u quicknotes -n 20 || true
+-- No entries --
+```
+
+## What would I do if QuickNotes shows 502 error?
+
+Well, firstly, i'll check logs in, for example, journalctl. Next I'll run `ss -tulpn | grep <port of my app>`, tracepath `<request to service>` and do some testing via `dig`
+
+## Task 2
+
+```
+ps -ef | grep quicknotes
+long1ta+   13357   13314  0 23:02 pts/1    00:00:00 /home/long1tail/.cache/go-build/d2/d2669b388084fca57ad8bc2e16f3aebe315b928221e2267b472e0af203e794e6-d/quicknotes
+long1ta+   13440   12297  0 23:03 pts/1    00:00:00 grep --color=auto quicknotes
+```
+
+I have 2 instanses running. Let's check, wich one of them listens on port
+
+```
+ss -tlnp | grep 8080
+LISTEN 0      4096               *:8080             *:*    users:(("quicknotes",pid=13357,fd=3))
+```
+
+As we can see, PID of listenning process is the PID of first running instance. Let's check if the service is available.
+
+```
+curl -s -o /dev/null -w "%{http_code}\n" http://localhost:8080/health
+200
+```
+
+Ok, servise looks available. let's check the bariers
+
+```
+sudo iptables -L -n -v 2>/dev/null || sudo nft list ruleset 2>/dev/null || true
+```
+I can't provide it's output because It contains a lot of of notes about my vpn server and it may cause vurnalabilities and private data leakage
+
+```
+dig +short localhost
+127.0.0.1
+```
+
+DNS is ok
+
+
+Summary
+I run a second QuickNotes instance on port 8080 failed because the port was already in use by the primary running instance. The deployment process does not verify whether the target port is already occupied. Since the application uses a fixed port configuration, concurrent launches can cause port conflicts.
+
+I can prevent such problems via docker usage and running by systemd