show errors

Show errors related to protocol violations.

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The show errors command displays errors that the load balancer generates when it detects protocol violations from the client or server.

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You can use Netcat, nc, to intentionally create a malformed HTTP message. In the example below, we create an HTTP request that has two Host headers:

bash
printf "GET / HTTP/1.1\r\nHost: 192.168.50.25\r\nHost:\r\n\r\n" | \
  nc 192.168.50.25 80

bash
printf "GET / HTTP/1.1\r\nHost: 192.168.50.25\r\nHost:\r\n\r\n" | \
  nc 192.168.50.25 80

output
bash
HTTP/1.1 400 Bad request
content-length: 90
cache-control: no-cache
content-type: text/html
connection: close
<html><body><h1>400 Bad request</h1>
Your browser sent an invalid request.

output
bash
HTTP/1.1 400 Bad request
content-length: 90
cache-control: no-cache
content-type: text/html
connection: close
<html><body><h1>400 Bad request</h1>
Your browser sent an invalid request.

Call show errors to see the event:

bash
echo "show errors" | \
  sudo socat stdio tcp4-connect:127.0.0.1:9999

bash
echo "show errors" | \
  sudo socat stdio tcp4-connect:127.0.0.1:9999

output
bash
Total events captured on [22/Feb/2021:18:43:07.052] : 1
[22/Feb/2021:18:43:02.909] frontend fe_main (#2): invalid request
   backend <NONE> (#-1), server <NONE> (#-1), event #0, src 192.168.50.25:59200
   buffer starts at 0 (including 0 out), 16338 free,
   len 46, wraps at 16336, error at position 42
   H1 connection flags 0x00000000, H1 stream flags 0x00000012
   H1 msg state MSG_HDR_L2_LWS(24), H1 msg flags 0x00001410
   H1 chunk len 0 bytes, H1 body len 0 bytes :
   
   00000  GET / HTTP/1.1\r\n
   00016  Host: 192.168.50.25\r\n
   00037  Host:\r\n
   00044  \r\n

output
bash
Total events captured on [22/Feb/2021:18:43:07.052] : 1
[22/Feb/2021:18:43:02.909] frontend fe_main (#2): invalid request
   backend <NONE> (#-1), server <NONE> (#-1), event #0, src 192.168.50.25:59200
   buffer starts at 0 (including 0 out), 16338 free,
   len 46, wraps at 16336, error at position 42
   H1 connection flags 0x00000000, H1 stream flags 0x00000012
   H1 msg state MSG_HDR_L2_LWS(24), H1 msg flags 0x00001410
   H1 chunk len 0 bytes, H1 body len 0 bytes :
   
   00000  GET / HTTP/1.1\r\n
   00016  Host: 192.168.50.25\r\n
   00037  Host:\r\n
   00044  \r\n

show errors

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