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Web / NGINX Interview questions

What is the difference between limit_req and limit_conn for rate limiting?

Both directives protect backends from being overwhelmed, but they limit different things.

limit_reqlimit_conn
Limits the rate of requests over time, e.g. 10 requests per second.Limits the number of simultaneous open connections per key.
Uses a leaky-bucket algorithm, can allow controlled bursts.Simple concurrent count, no time dimension.
Good against rapid-fire abuse like brute-force login attempts.Good against a client holding many connections open at once, e.g. slow downloads.

limit_req_zone $binary_remote_addr zone=one:10m rate=10r/s;
limit_conn_zone $binary_remote_addr zone=addr:10m;

server {
    location /login {
        limit_req zone=one burst=20 nodelay;
        limit_conn addr 5;
    }
}

They're frequently combined - limit_req to throttle how fast a client can hit an endpoint, and limit_conn to cap how many connections that client can hold open at the same time.

Which directive is better suited to stopping brute-force login attempts?
What algorithm does limit_req use to allow controlled bursts?

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Erlang

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