@newbie

Not sure why, but I didn't get an alert on this one, even though you tagged me.

WARNING - This is a long post :-).

The issue with FastCGI Cache is in how it works -- it can be a major performance gain, while also being a major pain if you don't know how it works.

The first thing to note is that FastCGI Cache caches the output of the page you see as a fully rendered page. If you were to visit a website, view the source, copy and paste that to a binary file, and then hit that page instead of a dynamically generated page, that's essentially FastCGI Caching (in very basic terms).

Why this matters is because of what it does. FastCGI Cache essentially strips away the dynamic aspect of your site when a cache hit is true and renders it as a static page.

Once this happens, until you clear the FastCGI Cache, requests for anything that has been previously cached will still be served. So if you made a mistake in your config, but FastCGI Cache was enabled when that mistake was made, the cache still runs and any request for a page still gets cached if it doesn't exist and isn't expired.

Without the fastcgi_cache_purge module, purging the cache has to be done by hand from the CLI. The issue here is that, from what I've read on their GitHub issues page, it doesn't work with the latest versions of NGINX. I've not tested this to confirm, though it's not the first time I've read this so I'm leaning towards it being true until I can test it on my own private Droplet. So until I can confirm, you'd need to test it or rely on clearing it manually.

So to clear the cache, if you're using /var/run/cache, you'd run:

rm -rf /var/run/cache/*

Which will delete everything in ./cache, but not ./cache itself.

...

What I Recommend

First, comment out the FastCGI setup. Until you get everything else working, having it active is going to cause issues.

Your configuration will end up looking like this:

#fastcgi_cache_path /var/run/cache levels=1:2 keys_zone=MYAPP:100m inactive=60m;
#fastcgi_cache_key "$scheme$request_method$host$request_uri";
#add_header X-Cache $upstream_cache_status;
#fastcgi_ignore_headers Cache-Control Expires Set-Cookie;

# Expires map
map $sent_http_content_type $expires {
    default                 off;
    text/html               epoch;
    text/css                30d;
    application/javascript  30d;
    ~image/                 max;
    font/woff2              max;
    font/woff               max;
    image/x-icon            max;
    application/font-woff2  max;
}

server {
    listen 80 default_server;
    listen [::]:80 default_server;

    expires $expires;

    server_name mydomain.com www.mydomain.com;

    # SSL configuration
    #
    # listen 443 ssl default_server;
    # listen [::]:443 ssl default_server;

    # include snippets/snakeoil.conf;

    root /var/www/html/website;

    # Add index.php to the list if you are using PHP
    index index.php index.html;

    if (!-e $request_filename) {
        rewrite /wp-admin$ $scheme://$host$uri/ permanent;  
        rewrite ^(/[^/]+)?(/wp-.*) $2 last;                     
        rewrite ^(/[^/]+)?(/.*\.php) $2 last;                   
    }

    #Cache everything by default
    #set $no_cache 0;

    #Don't cache POST requests
    #if ($request_method = POST) {
    #    set $no_cache 1;
    #}

    #Don't cache if the URL contains a query string
    #if ($query_string != "") {
    #    set $no_cache 1;
    #}

    #Don't cache the following URLs
    #if ($request_uri ~* "/wp-admin/|/xmlrpc.php|wp-.*.php|/feed/|index.php|sitemap(_index)?.xml") {
    #    set $no_cache 1;
    #}

    #Don't cache if there is a cookie called PHPSESSID
    #if ($http_cookie ~* "comment_author|wordpress_[a-f0-9]+|wp-postpass|wordpress_no_cache|wordpress_logged_in") {
    #    set $no_cache 1;
    #}

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

    location ~ \.php$ {
        fastcgi_split_path_info ^(.+\.php)(/.+)$;
        include snippets/fastcgi-php.conf;
        fastcgi_pass unix:/run/php/php7.0-fpm.sock;
        include fastcgi_params;
        fastcgi_param REQUEST_METHOD $request_method;
        fastcgi_param SCRIPT_FILENAME $document_root$fastcgi_script_name;
        #fastcgi_cache MYAPP;
        #fastcgi_cache_valid 200 60m;
        #fastcgi_cache_bypass $no_cache;
        #fastcgi_no_cache $no_cache;
    }

    location ~ /\.ht {
        deny all;
    }

    location /xmlrpc.php {
        deny all;
    }

    location = /favicon.ico { log_not_found off; access_log off; }
    location = /robots.txt { log_not_found off; access_log off; allow all; }
}

The next thing we need to look at is this:

        fastcgi_split_path_info ^(.+\.php)(/.+)$;
        include snippets/fastcgi-php.conf;
        fastcgi_pass unix:/run/php/php7.0-fpm.sock;
        include fastcgi_params;
        fastcgi_param REQUEST_METHOD $request_method;
        fastcgi_param SCRIPT_FILENAME $document_root$fastcgi_script_name;

I'd need to see:

snippets/fastcgi-php.conf

and

fastcgi_params

If either of this have redundant configuration, we need to fix that as with either of those, you shouldn't need:

        fastcgi_param REQUEST_METHOD $request_method;
        fastcgi_param SCRIPT_FILENAME $document_root$fastcgi_script_name;

Those should already exist in one of those files, but you most likely don't need both, so let's see what's inside each of those files (please note which file is which in your reply).