PageSpeed Serf fetch failure rate extremely high; only 4 of 12 recent fetches fully successful; is fetching working?

[Danrancan]

Hi, in I am running an Ubuntu 20.04 LEMP server with the following modules enabled:
ngx_http_brotli_filter_module.so, ngx_http_brotli_static_module.so, ngx_http_cache_purge_module.so ngx_http_modsecurity_module.so, ngx_http_security_headers_module.so, and ngx_pagespeed.so

In my Nginx error logs I am getting many messages similar to the following:
[error] 2924324#2982247: [ngx_pagespeed 1.15.0.0-8811] PageSpeed Serf fetch failure rate extremely high; only 7 of 18 recent fetches fully successful; is fetching working?

Can anyone help me understand what these errors mean and how exactly I can fix them?

Below is my nginx.conf file, my virtual host file, and my pagespeed.conf file.

#nginx.conf
user www-data;
worker_processes auto;
pid /run/nginx.pid;
#include /etc/nginx/modules-enabled/*.conf;
load_module modules/ngx_http_security_headers_module.so;
load_module modules/ngx_http_modsecurity_module.so;
load_module modules/ngx_pagespeed.so;
load_module modules/ngx_http_cache_purge_module.so;
load_module modules/ngx_http_brotli_filter_module.so;
load_module modules/ngx_http_brotli_static_module.so;

events {
	worker_connections 768;
	# multi_accept on;
}

http {
	##
	# Security Headers
	##

	security_headers on;
        hide_server_tokens on;

	##
	# Mod Security
	##

	modsecurity on;
	#modsecurity off;
	modsecurity_rules_file /etc/nginx/modsec/main.conf;

	##
	# Basic Settings
	##

	# Upload settings
	client_max_body_size 200M;
	client_body_buffer_size 200M;

	sendfile on;
	tcp_nopush on;
	tcp_nodelay on;
	types_hash_max_size 4096;
        server_tokens off;
        server_names_hash_bucket_size 64;
        #server_name_in_redirect off; # you might want to comment this out. Do some research.

        include /etc/nginx/mime.types;
        default_type application/octet-stream;

	##
	# Brotli Compression Settings
	##

	# The 'brotli off|on' value enables or disbles dynameic or on the fly compression of the content.
	brotli			on;
	# The 'brotli_static on' value enables the Nginx server to check if the pre-compressed files with the .br extensions
	# exist or not. The always value allows the server to send pre-compressed content without confirming if the browser
	# supports it or not. Since Brotli is resource-intensive, this modules is best suited to reduse the bottleneck situations.
	brotli_static		on;
	# The brotli_comp_level directive sets the dynamic compression quality. It can range from 0 to 11.
	brotli_comp_level	6;
        #brotli_window		512k;
	# Configure a minimum length in order to have the requst compressed, determined by the Content-Length field in the HTTP headers.
        #brotli_min_length       21; #20
	# Enable dynamic compression for specific MIME types, whereas text/html respnosese are always compressed.
	#brotli_types		application/atom+xml application/javascript application/json application/rss+xml application/vnd.ms-fontobject application/x-font-opentype application/x-font-truetype application/x-font-ttf application/x-javascript application/xhtml+xml application/xml font/eot font/opentype font/otf font/truetype image/svg+xml image/vnd.microsoft.icon image/x-icon image/x-win-bitmap text/css text/javascript text/plain text/xml;
	brotli_types application/atom+xml application/javascript application/json application/rss+xml
             application/vnd.ms-fontobject application/x-font-opentype application/x-font-truetype
             application/x-font-ttf application/x-javascript application/xhtml+xml application/xml
             font/eot font/opentype font/otf font/truetype image/svg+xml image/vnd.microsoft.icon
             image/x-icon image/x-win-bitmap text/css text/javascript text/plain text/xml;

	##
	# Gzip Compression Settings
	##

	#gzip off;
	# Linuxbabe turns gzip_vary on, but we turn it off here because when enabling it, you may have problems clearing the cache.
	#gzip_vary	off;
	#gzip_vary	on;
	#gzip_proxied	any;
	#gzip_min_length	1000;
	#gzip_comp_level	6;
	#gzip_buffers	16 8k;
	#gzip_http_version	1.1;
	# Linuxbabe (+ added extensions)
	#gzip_types	application/json application/x-javascript application/javascript application/atom+xml application/rss+xml application/vnd.ms-fontobject application/x-font-ttf application/x-web-app-manifest+json application/xhtml+xml application/xml;

	##
	# Proper Log Format for Netdata
	##

	# Create a custom Nginx log format called netdata that includes information about request_time, and upstream_response_time, measured in seconds with millisecond resolution.
	log_format netdata '$remote_addr - $remote_user [$time_local] '
	              '"$request" $status $body_bytes_sent '
	              '$request_length $request_time $upstream_response_time '
	              '"$http_referer" "$http_user_agent"';

	##
	# WebP Page Cache settings/conditional variables # Use this to enable SERVING webP images in nginx. Dont forget to add a location directive for webP in each virtual configuration files.
        ##

        #map $http_accept $webp_suffix {
          #default   "";
          #"~*webp"  ".webp";
        #}

	##
	# SSL Settings
	##

	ssl_session_cache	shared:SSL:10m;	#SSL session cache
	ssl_session_timeout	1h;
	ssl_prefer_server_ciphers	on;

	##
	# Logging Settings
	##

	access_log	/var/log/nginx/access.log;
	error_log	/var/log/nginx/error.log;

	##
	# FastCGI Cache (by Linuxbabe)
	##

	# Use this cache path for caching to disk not ram
	#fastcgi_cache_path	/usr/share/nginx/fastcgi_cache levels=1:2 keys_zone=phpcache:100m max_size=10g inactive=60m use_temp_path=off;
	# Use this cache path for caching to ram not disk
	fastcgi_cache_path      /usr/share/nginx/ramcache/fastcgi_temp/ levels=1:2 keys_zone=phpcache:100m max_size=2g inactive=60m use_temp_path=off;
	fastcgi_cache_key	"$scheme$request_method$host$request_uri";
	# By Easyengine.io
	# The line fastcgi_cache_use_stale is what makes caching on Nginx-side unique.
	# This line tells Nginx to use old (stale) cached version of page if PHP crashes. This is something not possible with WordPress caching plugins.
	fastcgi_cache_use_stale	error timeout invalid_header http_500;
	fastcgi_read_timeout 300;
	# The next 3 lines work with cacheing directly to ram
	# https://websiteforstudents.com/improve-nginx-cache-performance-with-tmpfs-on-ubuntu/
	#fastcgi_cache_revalidate on;
	#fastcgi_cache_background_update on;
	#fastcgi_ignore_headers Cache-Control Expires Set-Cookie;

	##
	# Virtual Host Configs
	##

	include	/etc/nginx/conf.d/*.conf;
	include	/etc/nginx/sites-enabled/*;
}

#virtualhost.conf file
server {
  listen 80;
  listen [::]:80;
  server_name mcmo.is www.mcmo.is;
  return 301 https://$host$request_uri;
}

server {
  listen 443 ssl http2;
  listen [::]:443 ssl http2;
  server_name mcmo.is  www.mcmo.is;
  root /var/www/mcmo.is/;

  ###
  # SSL (From Mozilla Config Generator: Modern Configuration)
  ###

  # Add Strict Transport Security Response Header with "always Paramater", to help prevent MITM attacks.
  # HSTS (ngx_http_headers_module is required) (63072000 seconds)
  add_header Strict-Transport-Security "max-age=63072000; includeSubDomains" always;
  ## Prevent click jacking by adding an X-Frame-Options header
  add_header x-frame-options "SAMEORIGIN" always;
  #add_header X-Frame-Options "SAMEORIGIN";
  # Add a content security policy header. First line is working original. 2nd line is from linuxbabe combined with working original.
  add_header Content-Security-Policy "frame-ancestors 'self';";
  #add_header Content-Security-Policy upgrade-insecure-requests "frame-ancestors 'self';";
  # Secure MIME Types with X-Content-Type-Options. Below line adds the X-Frame-Options header in Nginx.
  add_header X-Content-Type-Options nosniff;
  # Enable X-XSS-Protection header in Nginx
  add_header X-XSS-Protection "1; mode=block";
  add_header Referrer-Policy "strict-origin";
  add_header Permissions-Policy "geolocation=(),midi=(),sync-xhr=(),microphone=(),camera=(),magnetometer=(),gyroscope=(),fullscreen=(self),payment=()";
  # User recommendation from linuxbabe for fastcgi to keep working
  #fastcgi_ignore_headers Cache-Control Expires Set-Cookie; # already in nginx.conf

  # Path to signed certificate
  ssl_certificate /etc/letsencrypt/live/mcmo.is/fullchain.pem; # Managed by admin
  # Path to Intermediate certificates
  ssl_certificate_key /etc/letsencrypt/live/mcmo.is/privkey.pem; # Managed by admin
  # Verify chain of trust of OCSP response using Root CA and Intermediate certs
  ssl_trusted_certificate /etc/letsencrypt/live/mcmo.is/chain.pem; # Managed by admin
  # Perfect Forward Secrecy Diffie-Hellman 4098 parameters
  ssl_dhparam /etc/ssl/private/dhparams4096.pem; # Managed by admin

  # Mozilla Modern Compatibilty SSL configuration with OCSP stapling turned on and strict settings for A+ SSL Security rating
  ssl_protocols TLSv1.2 TLSv1.3; # Dropping SSLv3, ref: POODLERequires nginx >= 1.13.0 else use TLSv1.2 # Dropping TLSv1.1 for modern compatability.
  ssl_ciphers 'TLS_AES_128_GCM_SHA256:TLS_AES_256_GCM_SHA384:TLS_CHACHA20_POLY1305_SHA256:ECDHE-ECDSA-AES128-GCM-SHA256:ECDHE-RSA-AES128-GCM-SHA256:ECDHE-ECDSA-AES256-GCM-SHA384:ECDHE-RSA-AES256-GCM-SHA384:ECDHE-ECDSA-CHACHA20-POLY1305:ECDHE-RSA-CHACHA20-POLY1305:DHE-RSA-AES128-GCM-SHA256:DHE-RSA-AES256-GCM-SHA384';
  ssl_ecdh_curve secp384r1; # Requires nginx >= 1.1.0
  ssl_prefer_server_ciphers on;
  ssl_session_timeout 1d;
  ssl_session_cache shared:MozSSL:10m;  # about 40000 sessions
  ssl_session_tickets off;
  # OCSP stapling
  ssl_stapling on;
  ssl_stapling_verify on;
  resolver 8.8.8.8 8.8.4.4;

  ##
  # Harden nginx against DDOS

  ##
  # Pestmeester.nl # Change to 10 to really harden.
  ##

  client_header_timeout 15;
  client_body_timeout   15;
  keepalive_timeout     15;
  send_timeout          15;

  # Error & Access Logs
  access_log /var/log/nginx/mcmo.is.access.log netdata;
  error_log /var/log/nginx/mcmo.is.error.log warn;

  # Linuxbabe
  index index.php index.html index.htm index.nginx-debian.html;

  # Linuxbabe
  location / {
    try_files $uri $uri/ /index.php;
  }

  # Non-Linuxbabe
  #location / {
    #try_files $uri $uri/ /index.php?$args;
  #}

  # Non-Linuxbabe
  location ~ /.well-known {
    allow all;
  }

  # Non-Linuxbabe
  location = /favicon.ico {
    log_not_found off;
    access_log off;
  }

  # Non-Linuxbabe
  location = /robots.txt {
    allow all;
    log_not_found off;
    access_log off;
  }

  # Non-LinuxBabe (https://tonyteaches.tech/wepb-images-nginx/)
  # serve png, jpg, jpeg as webp if available
  #location ~* ^.+\.(png|jpe?g)$ {
    #add_header Vary Accept;
    #try_files $uri$webp_suffix $uri =404;
  #}

  # Linuxbabe
  location ~ ^/wp-json/ {
    rewrite ^/wp-json/(.*?)$ /?rest_route=/$1 last;
  }

  # Linuxbabe
  location ~* /wp-sitemap.*\.xml {
    try_files $uri $uri/ /index.php$is_args$args;
  }

  # Linuxbabe
  error_page 404 /404.html;
  error_page 500 502 503 504 /50x.html;

  # Linuxbabe
  location = /50x.html {
    root /usr/share/nginx/html;
  }

  ##
  # Pagespeed
  ##

  # enable pagespeed module on this server block
  pagespeed on;
  pagespeed Domain https://www.mcmo.is;
  pagespeed Domain https://mcmo.is;
  # Include UNIVERSAL Settings for Pagespeed Module
  include /etc/nginx/pagespeed.conf;

  # Non-Linuxbabe
  # Block access to xmlrpc.php file
  #location ~ /xmlrpc.php$ {
    #allow 192.168.30.0/24;
    #deny all;
    #error_page 403 =444;
    #include snippets/fastcgi-php.conf;
    #fastcgi_pass unix:/var/run/php/php7.4-fpm.sock;
  #}

  # Non-Linuxbabe
  # Only allow access of /admin via internal IP
  location ^~ /admin/ {
    allow 192.168.30.0/24;
    deny all;
    error_page 403 =444;
    include snippets/fastcgi-php.conf;
    fastcgi_pass unix:/var/run/php/php7.4-fpm.sock;
  }

  # Non-Linuxbabe
  # Allow local only to wp-login page
  #location ~ /wp-login.php {
    #allow 192.168.30.0/24;
    #deny all;
    #error_page 403 =444;
    #include snippets/fastcgi-php.conf;
    #fastcgi_pass unix:/var/run/php/php7.4-fpm.sock;
  #}

  # Non-Linuxbabe
  # Disallow PHP In Upload Folder
  location /wp-content/uploads/ {
    location ~ \.php$ {
    deny all;
    }
  }

  # Non-Linuxbabe
  # Security Settings For Better Privacy Deny Hidden Files
  location ~ /\. {
    deny all;
    access_log off;
    log_not_found off;
  }

  # Linuxbabe - disable access to hidden files
  location ~ /\.ht {
      access_log off;
      log_not_found off;
      deny all;
  }

  ##
  # FastCGI Cache
  ##

  # Cache Purging should be restricted to allowed IP addresses.
  # If not set, an attacker may be able to wipe your nginx fastcgi cache using simple GET requests. Linuxbabe (User Comment).
  # This (supposedly) enables cache purge but restricts it to your ip address and to your loopback address.
  location ~ /purge(/.*) {
    allow 127.0.0.1;
    allow 149.28.125.6; # Replace with your servers IPv4 address
    deny all;
    # Enable http-cache-purge module in nginx for above IP addresses
    fastcgi_cache_purge phpcache "$scheme$request_method$host$1";
  }

##
# START SKIP CACHE RULES: Prevent FastCGI caching for certain things/pages
##

set $skip_cache 0;

# POST requests and urls with a query string should always go to PHP
if ($request_method = POST) {
    set $skip_cache 1;
}
if ($query_string != "") {
    set $skip_cache 1;
}

# Don't cache uris containing the following segments
if ($request_uri ~* "/wp-admin/|/xmlrpc.php|wp-.*.php|^/feed/*|/tag/.*/feed/*|index.php|/.*sitemap.*\.(xml|xsl)") {
    set $skip_cache 1;
}

# Don't use the cache for logged in users or recent commenters
if ($http_cookie ~* "comment_author|wordpress_[a-f0-9]+|wp-postpass|wordpress_no_cache|wordpress_logged_in") {
    set $skip_cache 1;
}

# Sometimes I want to test the upstream (PHP-FPM and MariaDB) response time, so I also add the following lines to tell Nginx to bypass the FastCGI cache for my own IP addresses.
# Note: This was not fullly understood from linuxbabe tutorial fastcgi chapter, and therefore was modified by admin. Use carefully.
#if ($remote_addr ~* "108.231.125.253|108.231.125.253") {
#     set $skip_cache 1;
#}

# Skip the fastCGI Cache for ATNT Public IP, and the local network.
#if ($remote_addr ~* "108.231.125.253|108.231.125.254|192.168.30..*) {
#    set $skip_cache 1;
#}

# THIS IS THE MODIFIED CODE REFERENCED in 2 sections above from here.
# Lets deactivate it for now so that we don't bypass FastCGI Cache for our own IP, or fuck things up with modified lines.

#if ($remote_addr ~* "108.231.125.253|192.168.30..*") {
#    set $skip_cache 1;
#}

# IMPORTANT NOTE WITH SEO:
# If you use the Yoast SEO or Google XML Sitemap plugins to generate sitemap, then
# you also need to move the Yoast/Google XML rewrite rules below the skip cache rules.

##
# END SKIP CACHE RULES: Prevent FastCGI caching for certain things/pages
##

  # Linuxbabe
  # Pass Fastcgi to php
  location ~ \.php$ {
    fastcgi_pass unix:/run/php/php7.4-fpm.sock;
    fastcgi_param SCRIPT_FILENAME $document_root$fastcgi_script_name;
    include fastcgi_params;
    include snippets/fastcgi-php.conf;
    # Linuxbabe - FastCGI
    fastcgi_cache phpcache;
    fastcgi_cache_valid 200 301 302 60m;
    fastcgi_cache_use_stale error timeout updating invalid_header http_500 http_503;
    fastcgi_cache_min_uses 1;
    fastcgi_cache_lock on;
    # Tell Nginx to send request to upstream PHP-FPM server, instead of trying to find files in the cache.
    fastcgi_cache_bypass $skip_cache;
    # Tell Nginx not to cache the response.
    fastcgi_no_cache $skip_cache;
    add_header X-FastCGI-Cache $upstream_cache_status;
    add_header X-Content-Type-Options nosniff;
  }

  # Linuxbabe (Mostly, added some files extensions)
  # A long browser cache lifetime can speed up repeat visits to your page
  location ~* \.(jpg|ogg|ogv|svgz|eot|otf|mp4|rss|atom|zip|tgz|gz|rar|bz2|doc|doc|xls|exe|ppt|tar|mid|midi|wav|bmp|rtf|jpeg|gif|png|webp|svg|woff|woff2|ttf|css|js|ico|xml)$ {
    access_log        off;
    log_not_found     off;
    expires           360d;
  }
}

#pagespeed.conf file
##
# Pagespeed Module
##

# Linuxbabe
pagespeed Disallow                      "/wp-admin*"; # Boo's edit
pagespeed Disallow                      "/wp-login.php"; # Boo's edit
pagespeed Disallow                      "/admin/*"; # Boo's edit
pagespeed FetchHttps                    enable;
pagespeed NoTransformOptimizedImages    on;
pagespeed HttpCacheCompressionLevel     9;

#admin console
pagespeed Statistics on;
pagespeed StatisticsLogging on;
pagespeed LogDir /var/log/pagespeed;
pagespeed AdminPath /pagespeed_admin;

location ~ ^/pagespeed_admin {
   allow 127.0.0.1;
   allow 109.277.268.139; # Dans IP Address
   deny all;
}

# Where to cache files.
# Needs to exist and be writable by nginx. Use tmpfs for best performance.
pagespeed FileCachePath /usr/share/nginx/ramcache/ngx_pagespeed_temp;

# Ensure requests for pagespeed optimized resources go to the pagespeed handler
# and no extraneous headers get set.
location ~ "\.pagespeed\.([a-z]\.)?[a-z]{2}\.[^.]{10}\.[^.]+" {
  add_header "" "";
}
location ~ "^/pagespeed_static/" { }
location ~ "^/ngx_pagespeed_beacon$" { }

###
# Pagespeed Filters
###

# A good way to reduce CPU load is to change the default RewriteLevel to
# PassThrough, which disables all PageSpeed filters.
# Then you can enable the filter you need.
pagespeed RewriteLevel                  CoreFilters;
#pagespeed RewriteLevel                 PassThrough;
#pagespeed RewriteLevel                 OptimizeForBandwidth;

## Text / HTML
#pagespeed EnableFilters                 add_head; # Core Filter
#pagespeed EnableFilters                 remove_quotes; # Core Filter
#pagespeed EnableFilters                 combine_heads;
pagespeed EnableFilters                 insert_dns_prefetch; # Extras # Linuxbabe Recommendation
pagespeed EnableFilters                 collapse_whitespace; # Extras # Linuxbabe Recommendation
#pagespeed EnableFilters                 convert_meta_tags; # Core Filter
#pagespeed EnableFilters                 elide_attributes;
#pagespeed EnableFilters                 pedantic;
#pagespeed EnableFilters                 remove_comments;
#pagespeed EnableFilters                 remove_quotes;
pagespeed EnableFilters                 trim_urls;

## JavaScript
#This filter is likely to cause problems for loading your web pages.
pagespeed EnableFilters			defer_javascript; # Extras # Linuxbabe Recommendation
#pagespeed EnableFilters                 combine_javascript; # Core Filter
#pagespeed EnableFilters                 canonicalize_javascript_libraries;
#pagespeed EnableFilters                 inline_javascript; # Core Filter
pagespeed EnableFilters                 rewrite_javascript; # Extras # Core Filter according to linuxbabe

## CSS
#pagespeed EnableFilters                 outline_css;
#pagespeed EnableFilters                 flatten_css_imports; # Core Filter
#pagespeed EnableFilters                 combine_css; # Core Filter
#pagespeed EnableFilters                 inline_import_to_link; # Core Filter
#pagespeed EnableFilters                 inline_css; # Core Filter
pagespeed EnableFilters                 inline_google_font_css;
#pagespeed EnableFilters                 move_css_above_scripts;
#pagespeed EnableFilters                 move_css_to_head;
pagespeed EnableFilters                 prioritize_critical_css; # Extras # Linuxbabe Recommendation
#pagespeed EnableFilters                 rewrite_css; # Core Filter
#pagespeed EnableFilters                 fallback_rewrite_css_urls; # Core Filter
#pagespeed EnableFilters                 rewrite_style_attributes_with_url; # Core Filter

## Images
pagespeed EnableFilters                 recompress_images;
pagespeed EnableFilters                 rewrite_images; # Core Filter # Filter group
pagespeed EnableFilters                 responsive_images; # Extras
pagespeed EnableFilters                 dedup_inlined_images; # Extras
pagespeed EnableFilters                 inline_preview_images; # Extras
pagespeed EnableFilters                 resize_mobile_images; # Extras
#pagespeed EnableFilters                 lazyload_images; # Extras # Turn off with wordpress
pagespeed EnableFilters                 inline_images;
#pagespeed EnableFilters                 convert_gif_to_png;
pagespeed EnableFilters                 convert_jpeg_to_progressive;
pagespeed EnableFilters                 recompress_jpeg;
pagespeed EnableFilters                 recompress_png;
pagespeed EnableFilters                 recompress_webp;
#pagespeed EnableFilters                 strip_image_color_profile;
pagespeed EnableFilters                 strip_image_meta_data;
pagespeed EnableFilters                 jpeg_subsampling;
pagespeed EnableFilters                 convert_png_to_jpeg;
pagespeed EnableFilters                 resize_images; # Extras #Linuxbabe recommendation on passthrough
#pagespeed EnableFilters                 resize_rendered_image_dimensions;
pagespeed EnableFilters                 convert_jpeg_to_webp; # Linuxbabe recommendation on passthrough
pagespeed EnableFilters                 convert_to_webp_lossless; # Linuxbabe recommendation on passthrough
pagespeed EnableFilters                 insert_image_dimensions;
pagespeed NoTransformOptimizedImages    on;
#pagespeed EnableFilters                 sprite_images; # Extras

## Other
pagespeed EnableFilters                 hint_preload_subresources;
#pagespeed EnableFilters                 extend_cache; # Core Filter
pagespeed EnableFilters                 in_place_optimize_for_browser;

If anyone can take a look at these files and tell me exactly what the issue is and how I can fix pagespeed, it would be greatly appreciated! Thank you so much!

Dan

[Lofesa]

Hi

The error message tell us that Serf is not working. Serf is the headless browser pagespeed uses for fecht the resources.

About you config:

pagespeed HttpCacheCompressionLevel 9;

This line makes pagespeed to store optimized resources gziped, and serve it as gzip. To serve it with brotli compression you need to set it to 0, then optimized resources are stored w/o compression and brotli compress it on the fly.

pagespeed Domain https://www.mcmo.is;
pagespeed Domain https://mcmo.is;

These lines can be simplified:
pagespeed Domain http*://*.mcmo.is;
This cover http and https versions of a url and all subdomains and the main domain.

And the most probable error origin is:

pagespeed FetchHttps enable;

This MUST be set with this other line:

pagespeed SslCertDirectory directory;

where directory, in a default ubuntu/debian distro is:

/etc/ssl/certs

Think in Serf as a browser, it need the CA root or intermediates certificates to validate the certificates your web server uses.

An altertative to fecht https resources is:

pagespeed LoadFromFile "https://www.mcmo.is" "/var/www/mcmo.is";
pagespeed ImplicitCacheTtlMs implicit_cache_ttl_in_milliseconds;

Read these:
https://www.modpagespeed.com/doc/domains#ModPagespeedLoadFromFile
https://www.modpagespeed.com/doc/system#implicit_cache_ttl