Sometimes it is very difficult to analyse the HaProxy Logs manually . Very few people know about the small tool name halog , it gets shipped with HaProxy itself.
HALog is a small and very powerful tool to analyze HaProxy log lines.Installation is pretty simple, as described bellow:
cd /usr/src
wget http://haproxy.1wt.eu/download/1.5/src/devel/haproxy-1.5-dev11.tar.gz
tar xzf haproxy-1.5-dev11.tar.gz
cd haproxy-1.5-dev11/contrib/halog
make
cp halog /usr/bin/
and we are done and ready to analyse the HaProxy Logs. Below are few examples
List servers by number of requests treated
The command below lists the servers by the number of requests they treated. The server name is
prefixed by the backend name.

The eighth columns “tot_req” gives the number of requests treated by the server.

cat filename.log | halog -srv -H -q |awk ’NR==1; NR > 1 {print $0 | “sort -n -r -k 9”}’ |column -t

2. List servers by response time

The command below lists the servers by response time. The server name is prefixed by the backend
name.
The response time is in milliseconds and the latest columns “avg_rt” gives the average response time
for all the URLs forwarded to this server in this backend.

cat filename.log | halog -srv -H -q |awk ’NR==1; NR > 1 {print $0 | “sort -n -r -k 12”}’ |column -t

3. List servers by application errors: HTTP status code 5xx

The command below lists the servers by number of application errors. The server name is prefixed by
the backend name.
The sixth column “5xx” gives the number of application errors generated by the server.

cat filename.log |halog -srv -H -q | awk ’NR==1; NR > 1 {print $0 | “sort -n -r -k 6”}’ | column -t

4. List servers by errors

The command below lists the servers by number of errors not related to the application. The server
name is prefixed by the backend name.

cat filename.log |halog -srv -H -q | awk ’NR==1; NR > 1 {print $0 | “sort -n -r -k 5”}’ | column -t

5. List URLs by server computation time
The command below lists the URLs by the average computation time, whatever the server which treated
it.
The sixth column “okavg” provides the URL average computation time in milliseconds.

cat filename.log | halog -ut -H -q | column -t

6. List URLs by errors

The command below lists the URLs by the number of errors they have generated, whatever the server
which treated it or the type of error.
The second column “err” provides the number of errors generated by the given URL (latest column).

cat filename.log | halog -ue -H -q | column -t

7 . List URLs by missing files: HTTP status code 404
The command below lists the URLs by the number of missing files error they have generated, whatever
the server which treated it.
The first column “req” provides the number of 404 returned for the given URL (latest column).

cat filename.log | halog -u -H -q -hs 404 | column -t

8. List URLs by number of request
The command below lists the URLs by the number of time they have been requested on the platform.
The first column “req” provides the number of time the URLs was called.

cat filename.log | halog -u -H -q | awk ’NR==1; NR > 1 {print $0 | “sort -n -r -k 1”}’ | column -t