Nginx fails to start HTTP/2 server due to error: unknown log format

Question

In our hosting server from the Plesk cpanel, Nginx is configured to work as a reverse proxy engine. As I need to enable HTTP/2 that can speed up the loading time of Plesk and hosted websites. Additionally, using HTTP/2 is more secure because it makes TLS connections mandatory

When I tried to enable HTTP/2 from GUI it gave the error as:

[2018-11-15 10:47:29.068] ERR [util_exec] proc_close() failed ['/opt/psa/admin/bin/nginx_control' '--start'] with exit code [1] Can not start proxy server: /opt/psa/admin/sbin/nginx-config execution failed: nginx: [emerg] unknown log format "main" in /etc/nginx/nginx.conf:26 nginx: configuration file /etc/nginx/nginx.conf test failed

Here is my configuration of nginx.conf file

#user  nginx;
worker_processes  1;

error_log  /var/log/nginx/error.log;
error_log  /var/log/nginx/error.log  notice;
error_log  /var/log/nginx/error.log  info;

#pid        /var/run/nginx.pid;

include /etc/nginx/modules.conf.d/*.conf;

events {
    worker_connections  1024;
}


http {
    include       mime.types;
    default_type  application/octet-stream;

    #log_format  main  '$remote_addr - $remote_user [$time_local] "$request" '
    #                  '$status $body_bytes_sent "$http_referer" '
    #                  '"$http_user_agent" "$http_x_forwarded_for"';

    access_log  /var/log/nginx/access.log  main;

    sendfile        on;
    #tcp_nopush     on;

    #keepalive_timeout  0;
    keepalive_timeout  65;
    #tcp_nodelay        on;

    #gzip  on;
    #gzip_disable "MSIE [1-6]\.(?!.*SV1)";

    server_tokens off;

    include /etc/nginx/conf.d/*.conf;
}

# override global parameters e.g. worker_rlimit_nofile
include /etc/nginx/*global_params;

How do we Enable HTTP/2

Solution

The main reason for the failure was that I had explicitly commented out log_format main.

Configuring Access Logs in Nginx Under Nginx, all client requests to the server are recorded in the access log in a specified format using the ngx_http_log_module module.

The default log file is log/access.log (usually /var/log/nginx/access_log on Linux systems) and the default format for logging is normally the combined or main format (this can vary from one distro to another).

The access_log directive (applicable in the HTTP, server, location, if in location and limit except for context) is used to set the log file and the log_format directive (applicable under the HTTP context only) is used to set the log format. The log format is described by common variables and variables that generated only at the time when a log is written.

The syntax for configuring a log format is:

log_format format_name 'set_of_variables_to_define_format';

---

/etc/ngnix/ngnix.conf

#user  nginx;
worker_processes  1;

error_log  /var/log/nginx/error.log;
error_log  /var/log/nginx/error.log  notice;
error_log  /var/log/nginx/error.log  info;

#pid        /var/run/nginx.pid;

include /etc/nginx/modules.conf.d/*.conf;

events {
    worker_connections  1024;
}


http {
    include       mime.types;
    default_type  application/octet-stream;

    log_format  main  '$remote_addr - $remote_user [$time_local] "$request" '
                      '$status $body_bytes_sent "$http_referer" '
                      '"$http_user_agent" "$http_x_forwarded_for"';

    access_log  /var/log/nginx/access.log  main;

    sendfile        on;
    #tcp_nopush     on;

    #keepalive_timeout  0;
    keepalive_timeout  65;
    #tcp_nodelay        on;

    #gzip  on;
    #gzip_disable "MSIE [1-6]\.(?!.*SV1)";

    server_tokens off;

    include /etc/nginx/conf.d/*.conf;
}

# override global parameters e.g. worker_rlimit_nofile
include /etc/nginx/*global_params;

It worked

"Additionally, using HTTP/2 is more secure because it makes TLS connections mandatory" - This statement is wrong. The relevant part is not if HTTP/2 is enabled at the server but if the URL is http:// or https://. In the first case, it will use plain HTTP/1.1, in the second case HTTP/1.1 or HTTP/2 over TLS depending on what the server supports.