By default Ghost adds headers that effectively forbid caching, because the default cache-control header has a lifetime (max-age) set of 0. So lets change that first:

Add a caching config to the ghost config.production.json file (see https://ghost.org/docs/config/#caching for full details):

"caching": {
  "frontend": {
    "maxAge": 60
  },
  "contentAPI": {
    "maxAge": 60
  }
}

Then go into the nginx config file for the site (the one that ghost-cli created in /etc/nginx/sites-available/) and add the bare minimum, because by nginx has quite good default values for many cache options.

1. Give nginx a place to store the cached files, eg in /tmp

proxy_cache_path /tmp/nginx_ghost levels=1:2 keys_zone=ghostcache:10m max_size=100m inactive=24h;

2. Within the existing location block that does the reverse proxying, lets do these four things:

• enable the caching (proxy_cache ghostcache;)
• protect the poor ghost instance that only one request for each cache key hit it (proxy_cache_lock on;)
• allow it to update the cache during serving „outdated entries“ (proxy_cache_background_update on;)
• continue to serve cached content even if ghost should fall over (proxy_cache_use_stale ...)

proxy_cache ghostcache;
proxy_cache_lock on;
proxy_cache_background_update on;
proxy_cache_use_stale updating error timeout http_500 http_502 http_429;

3. Lastly, to see it in action, lets add a header that puts the cache status into it so that we can see it from the browser dev tools:

add_header X-Cache-Status $upstream_cache_status;

And thats already it, restart ghost (to activate the config), reload nginx:

sudo systemctl restart ghost...
sudo systemctl reload nginx

Just for completeness, my full nginx config then looks like this:

proxy_cache_path /tmp/nginx_ghost levels=1:2 keys_zone=ghostcache:10m max_size=100m inactive=24h;

map $status $header_content_type_options {
    204 "";
    default "nosniff";
}

server {
    listen 443 ssl http2;
    listen [::]:443 ssl http2;

    server_name blog.settgast.org;
    root /var/www/blog/system/nginx-root; # Used for acme.sh SSL verification (https://acme.sh)

    ssl_certificate /etc/letsencrypt/blog.settgast.org/fullchain.cer;
    ssl_certificate_key /etc/letsencrypt/blog.settgast.org/blog.settgast.org.key;
    include /etc/nginx/snippets/ssl-params.conf;

    location / {
        proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
        proxy_set_header X-Forwarded-Proto $scheme;
        proxy_set_header X-Real-IP $remote_addr;
        proxy_set_header Host $http_host;
        proxy_pass http://127.0.0.1:2368;

	add_header X-Content-Type-Options $header_content_type_options;

	proxy_cache ghostcache;
	proxy_cache_lock on;
	proxy_cache_background_update on;
	proxy_cache_use_stale updating error timeout http_500 http_502 http_429;
	add_header X-Cache-Status $upstream_cache_status;
    }

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

    client_max_body_size 1g;
}

Benchmarking

To benchmark it a bit, lets use the wrk tool and hit ghost with 500 parallel connections, once default without caching, once with caching enabled:

As a baseline I ran it without the caching, so in default mode:

wrk -c 500 -t 4 https://blog.settgast.org/caching-for-ghost-nginx-edition/
Running 10s test @ https://blog.settgast.org/caching-for-ghost-nginx-edition/
  4 threads and 500 connections
  Thread Stats   Avg      Stdev     Max   +/- Stdev
    Latency     1.13s   507.40ms   1.99s    58.33%
    Req/Sec    22.18     15.36    60.00     61.22%
  371 requests in 10.08s, 5.53MB read
  Socket errors: connect 0, read 0, write 0, timeout 311
Requests/sec:     36.80
Transfer/sec:    561.85KB

36 requests per second, thats not much. Or to put it differently: From the 500 connections started, only 371 completed within 10 seconds, the others were still loading.

Now lets repeat this with NGINX caching enabled:

wrk -c 500 -t 4 https://blog.settgast.org/caching-for-ghost-nginx-edition/
Running 10s test @ https://blog.settgast.org/caching-for-ghost-nginx-edition/
  4 threads and 500 connections
  Thread Stats   Avg      Stdev     Max   +/- Stdev
    Latency    41.36ms   70.71ms   1.05s    93.24%
    Req/Sec     3.84k   804.38     5.36k    83.79%
  139524 requests in 10.06s, 1.95GB read
Requests/sec:  13865.81
Transfer/sec:    198.63MB

Over 13 thousand requests per second from a small VPS (2CPUs, 4GB RAM), or a factor of 380 times more requests!

References

• Elenas great series on self-hosting Ghost and adding caching: https://aseachange.com/@elena
• This blog post on how nginx caching works: https://www.sheshbabu.com/posts/nginx-caching-proxy/
• The official docs for nginx helped a lot: https://docs.nginx.com/nginx/admin-guide/content-cache/content-caching/
• Scotts article was also an inspiration: https://scotthelme.co.uk/caching-ghost-with-nginx/