Enable FCGI cache in Nginx

To enable fcgi cache in Nginx, add the following code outside the server block.

fastcgi_cache_path /var/run/nginx-fastcgi-cache levels=1:2 keys_zone=SOKCACHE:60m inactive=60m;
fastcgi_cache_key "$scheme$request_method$host$request_uri";
fastcgi_cache_use_stale error timeout invalid_header http_500;
fastcgi_ignore_headers Cache-Control Expires Set-Cookie;

Inside your location for .php files, above the proxy_pass, add

# cache start
fastcgi_cache_bypass $skip_cache;
fastcgi_no_cache $skip_cache;
fastcgi_cache SOKCACHE;
fastcgi_cache_valid 60m;
add_header X-FastCGI-Cache $upstream_cache_status;
# cache end

Add below code above .php location block

# Cache start

set $skip_cache 0;

if ($request_method = POST) {
    set $skip_cache 1;
}

if ($query_string != "") {
    set $skip_cache 1;
}

if ($request_uri ~* "/wp-admin/|/xmlrpc.php|wp-.*.php|/feed/|index.php|sitemap(_index)?.xml") {
    set $skip_cache 1;
}  

if ($http_cookie ~* "comment_author|wordpress_[a-f0-9]+|wp-postpass|wordpress_no_cache|wordpress_logged_in") {
    set $skip_cache 1;
}

# Cache end

This is used to skip FCGI cache for logged-in users.

Example

fastcgi_cache_path /var/run/nginx-fastcgi-cache levels=1:2 keys_zone=SOKCACHE:60m inactive=60m;
fastcgi_cache_key "$scheme$request_method$host$request_uri";
fastcgi_cache_use_stale error timeout invalid_header http_500;
fastcgi_ignore_headers Cache-Control Expires Set-Cookie;

server {
    listen 80;
    listen 443 ssl http2;
    ssl_certificate /etc/ssl/serverok.in.crt;
    ssl_certificate_key /etc/ssl/serverok.in.key;
    server_name serverok.in www.serverok.in;
    root /home/serverok.in/html/;
    index index.php index.html index.htm;
    access_log /var/log/nginx/serverok.in.log;
    error_log /var/log/nginx/serverok.in-error.log;
    client_max_body_size 1000M;
    proxy_read_timeout 600s;
    fastcgi_read_timeout 600s;
    fastcgi_send_timeout 600s;

    # Rewrites for Yoast SEO XML Sitemap

    rewrite ^/sitemap.xml$ /index.php?sitemap=1 last;
    rewrite ^/sitemap_index.xml$ /index.php?sitemap=1 last;
    rewrite ^/([^/]+?)-sitemap([0-9]+)?.xml$ /index.php?sitemap=$1&sitemap_n=$2 last;

    # Forbidden files or directories
    location ~ ^/(\.user.ini|\.htaccess|\.git|\.svn|\.project|\.env) {
        return 404;
    }

    location = /favicon.ico {
        log_not_found off;
        access_log off;
    }

    location = /robots.txt {
        allow all;
        log_not_found off;
        access_log off;
        try_files $uri /index.php?$args;
    }

    location = /xmlrpc.php {
        deny all;
        access_log off;
        log_not_found off;
    }

    # Cache start

    set $skip_cache 0;

    if ($request_method = POST) {
        set $skip_cache 1;
    }

    if ($query_string != "") {
        set $skip_cache 1;
    }

    if ($request_uri ~* "/wp-admin/|/xmlrpc.php|wp-.*.php|/feed/|index.php|sitemap(_index)?.xml") {
        set $skip_cache 1;
    }  

    if ($http_cookie ~* "comment_author|wordpress_[a-f0-9]+|wp-postpass|wordpress_no_cache|wordpress_logged_in") {
        set $skip_cache 1;
    }

    # Cache end

    location /nginx_status {
        stub_status;
    }

    location / {
            try_files $uri $uri/ /index.php?$args;
    }

    location ~ \.php$ {
        include snippets/fastcgi-php.conf;
        fastcgi_intercept_errors on;
        fastcgi_buffer_size 128k;
        fastcgi_buffers 256 16k;
        fastcgi_busy_buffers_size 256k;
        fastcgi_temp_file_write_size 256k;
        fastcgi_send_timeout 600;
        fastcgi_read_timeout 600;
        fastcgi_param HTTP_PROXY "";
        fastcgi_pass unix:/run/php/php-fpm-serverok.sock;
        # cache start
        fastcgi_cache_bypass $skip_cache;
        fastcgi_no_cache $skip_cache;
        fastcgi_cache SOKCACHE;
        fastcgi_cache_valid 60m;
        add_header X-FastCGI-Cache $upstream_cache_status;
        # cache end
    }

    location ~* \.(txt|xml|js)$ {
            expires max;
            log_not_found off;
            access_log off;
    }

    location ~* \.(css)$ {
            expires max;
            log_not_found off;
            access_log off;
    }

    location ~* \.(flv|ico|pdf|avi|mov|ppt|doc|mp3|wmv|wav|mp4|m4v|ogg|webm|aac|eot|ttf|otf|woff|svg)$ {
            expires max;
            log_not_found off;
            access_log off;
    }

    location ~* \.(jpg|jpeg|png|gif|swf|webp)$ {
             expires max;
             log_not_found off;
             access_log off;
    }
    
    location /wp-content/themes/understrap-child/.git/ {
        return 404;
    }
    
    gzip on;
    gzip_http_version  1.1;
    gzip_comp_level    5;
    gzip_min_length    256;
    gzip_proxied       any;
    gzip_vary          on;
    gzip_types
        application/atom+xml
        application/javascript
        application/x-javascript
        application/json
        application/rss+xml
        application/vnd.ms-fontobject
        application/x-font-ttf
        application/x-web-app-manifest+json
        application/xhtml+xml
        application/xml
        font/opentype
        image/svg+xml
        image/x-icon
        text/css
        text/plain
        text/x-component;
}