Proxy cache basics in Nginx - Step-by-Step Execution

Process Flow - Proxy cache basics

Client sends request

↓

Nginx receives request

↓

Check cache for response

↓

Serve cached

↓

Return response

↓

Return response

Nginx checks if a cached response exists for a client request. If yes, it serves the cached response. If no, it fetches from the upstream server, caches it, then returns it.

Execution Sample

Nginx

proxy_cache_path /tmp/cache keys_zone=mycache:10m;
server {
  location / {
    proxy_cache mycache;
    proxy_pass http://backend;
  }
}

This config sets up a cache zone and enables proxy caching for requests to the backend server.

Process Table

Step	Action	Cache Check	Cache Hit?	Result
1	Client sends request for /index.html	N/A	N/A	Request received by Nginx
2	Nginx checks cache for /index.html	Look in /tmp/cache	No	Cache miss, fetch from backend
3	Nginx requests /index.html from backend	N/A	N/A	Backend responds with content
4	Nginx stores response in cache	Write to /tmp/cache	N/A	Response cached
5	Nginx returns response to client	N/A	N/A	Client receives fresh content
6	Client sends request for /index.html again	N/A	N/A	Request received by Nginx
7	Nginx checks cache for /index.html	Look in /tmp/cache	Yes	Cache hit, serve cached content
8	Nginx returns cached response to client	N/A	N/A	Client receives cached content

💡 Execution stops after serving cached content on second request.

Status Tracker

Variable	Start	After Step 2	After Step 4	After Step 7	Final
cache for /index.html	empty	miss	stored	hit	hit

Key Moments - 3 Insights

Why does Nginx fetch from backend on the first request?

Because the cache is empty at first (see execution_table step 2 shows cache miss), so Nginx must get fresh content.

How does Nginx know when to serve cached content?

It checks the cache for the requested URL (step 7 shows cache hit), then serves cached content without contacting backend.

What happens after Nginx fetches content from backend?

Nginx stores the response in cache (step 4) so future requests can be served faster.

Visual Quiz - 3 Questions

Look at the execution_table, what is the cache status at Step 2?

A Cache miss

B Cache hit

C Cache storing

D Cache empty

💡 Hint

Check the 'Cache Hit?' column at Step 2 in execution_table.

At which step does Nginx store the response in cache?

A Step 3

B Step 4

C Step 5

D Step 7

💡 Hint

Look for the action 'stores response in cache' in execution_table.

If the cache was never stored, what would happen at Step 7?

A Return error

B Cache hit

C Cache miss

D Serve stale content

💡 Hint

Refer to variable_tracker for cache state after Step 4 and Step 7.

Concept Snapshot

proxy_cache_path sets cache location and size.
proxy_cache enables caching in location.
Nginx checks cache before fetching upstream.
Cache hit serves cached content fast.
Cache miss fetches and stores response.
Improves performance and reduces backend load.

Full Transcript

Proxy cache basics in Nginx means saving responses from backend servers so future requests can be served quickly from cache. When a client sends a request, Nginx first looks in its cache. If the response is there (cache hit), it sends it immediately. If not (cache miss), Nginx fetches the response from the backend, stores it in cache, then returns it to the client. This process speeds up responses and reduces backend work. The example config shows how to set up a cache zone and enable proxy caching. The execution table traces two requests: the first misses cache and stores response; the second hits cache and serves cached content. Variables track cache state changes. Key moments clarify why cache miss happens first and how cache hit works later. The quiz tests understanding of cache status and steps. The snapshot summarizes the main points for quick recall.