Nginx cache file is too small

[kkobylyanskiy]

Hi, 
I'm using Nginx as a reverse-proxy to cache my POST request and wrote the
following config:

http {
    gzip on;
    gzip_proxied any;
    gzip_types text/plain application/json;
    gzip_min_length 1000;
    proxy_cache_path /var/cache/nginx levels=1:2 keys_zone=FLOWS:100m
inactive=24h max_size=2g use_temp_path=off;
    server {
        listen 3200;
        location /api/flows-page-v1 {
            proxy_pass              http://app:3000/api/flows-page-v1;
            proxy_set_header        Host $host;
            proxy_buffering         on;
            proxy_cache             FLOWS;
            proxy_cache_methods     POST;
            proxy_cache_key         "$request_uri|$request_body";
            proxy_cache_valid       200 1d;
            client_body_buffer_size 512k;
            proxy_buffers           6 128k;
            proxy_buffer_size       512k;
            proxy_busy_buffers_size 512k;
            proxy_cache_use_stale   error timeout invalid_header updating
                                    http_500 http_502 http_503 http_504;
            add_header X-Cached     $upstream_cache_status;
        }
    }
} 
I'm getting the following error when trying so send a request for the second
time after the first on is cached:

[crit] 20#20: *2 cache file
"/var/cache/nginx/6/fb/bee5677b8b46add7cfef279105773fb6" is too small
I logged in to the container and verified that this file contains cached
content.

>From the source code it seems like the following fragment causes this error
and therefore cache MISS (nginx/src/http/ngx_http_file_cache.c):

if ((size_t) n < c->header_start) {
    ngx_log_error(NGX_LOG_CRIT, r->connection->log, 0,
                  "cache file \"%s\" is too small", c->file.name.data);
    return NGX_DECLINED;
}

I already found the similar question -
https://forum.nginx.org/read.php?2,271756 but the answer doesn't seem to be
related to my situation: I run nginx in docker-compose, therefore there is
no any temporary files left in the cache directories, as well as the other
nginx process.

What should I do to avoid this error?

Posted at Nginx Forum: https://forum.nginx.org/read.php?2,291344,291344#msg-291344