Por que o nginx não atende à solicitação Cache-Control do cliente?

Tenho uma diretiva de cache no meu balanceador nginx sem nenhuma configuração específica.
Vejo que quando pressiono CTRL-F5 no meu navegador, todos os recursos são solicitados com Cache-Control:no-cachecabeçalhos, mas o nginx ainda responde com conteúdo em cache.

É por design que o nginx honra apenas o cabeçalho de cache do servidor de backend e não o do cliente?

Esta é a parte relevante da configuração de cache do nginx:

  proxy_cache_path /var/cache/nginx levels=1:2 keys_zone=mycache:100m max_size=500m inactive=60m use_temp_path=off;
  proxy_cache_key $host$request_uri;

  proxy_cache mycache;
  add_header X-Cache-Status $upstream_cache_status;

Os valores X-Cache-Status são HIT mesmo que o Cache-Control do cliente não seja cache

Esta é a configuração completa:

# configuration file /etc/nginx/nginx.conf:
user www-data;
worker_processes auto;
pid /run/nginx.pid;
include /etc/nginx/modules-enabled/*.conf;

events {
    worker_connections 768;
    # multi_accept on;
}

http {

    ##
    # Basic Settings
    ##

    sendfile on;
    tcp_nopush on;
    types_hash_max_size 2048;
    server_tokens off;
    client_max_body_size 100M;

    # server_names_hash_bucket_size 64;
    # server_name_in_redirect off;

    include /etc/nginx/mime.types;
    default_type application/octet-stream;

    ##
    # SSL Settings
    ##

    ssl_protocols TLSv1 TLSv1.1 TLSv1.2 TLSv1.3; # Dropping SSLv3, ref: POODLE
    ssl_prefer_server_ciphers on;

    ##
    # Logging Settings
    ##

    log_format cache_st '$remote_addr - $upstream_cache_status [$time_local] "$request" $status $body_bytes_sent "$http_referer" "$http_user_agent"';
    access_log /var/log/nginx/access.log cache_st;
    error_log /var/log/nginx/error.log;

    ##
    # Gzip Settings
    ##

    gzip on;

    # gzip_vary on;
    # gzip_proxied any;
    # gzip_comp_level 6;
    # gzip_buffers 16 8k;
    # gzip_http_version 1.1;
    # gzip_types text/plain text/css application/json application/javascript text/xml application/xml application/xml+rss text/javascript;

    #
    ## Cache
    #
    
    proxy_cache_path /var/cache/nginx levels=1:2 keys_zone=mycache:100m max_size=500m inactive=60m use_temp_path=off;


    ##
    # Virtual Host Configs
    ##

    include /etc/nginx/conf.d/*.conf;
    include /etc/nginx/sites-enabled/*;
}


#mail {
#   # See sample authentication script at:
#   # http://wiki.nginx.org/ImapAuthenticateWithApachePhpScript
#
#   # auth_http localhost/auth.php;
#   # pop3_capabilities "TOP" "USER";
#   # imap_capabilities "IMAP4rev1" "UIDPLUS";
#
#   server {
#       listen     localhost:110;
#       protocol   pop3;
#       proxy      on;
#   }
#
#   server {
#       listen     localhost:143;
#       protocol   imap;
#       proxy      on;
#   }
#}

# configuration file /etc/nginx/modules-enabled/50-mod-http-auth-pam.conf:
load_module modules/ngx_http_auth_pam_module.so;

# configuration file /etc/nginx/modules-enabled/50-mod-http-cache-purge.conf:
load_module modules/ngx_http_cache_purge_module.so;

# configuration file /etc/nginx/modules-enabled/50-mod-http-dav-ext.conf:
load_module modules/ngx_http_dav_ext_module.so;

# configuration file /etc/nginx/modules-enabled/50-mod-http-echo.conf:
load_module modules/ngx_http_echo_module.so;

# configuration file /etc/nginx/modules-enabled/50-mod-http-fancyindex.conf:
load_module modules/ngx_http_fancyindex_module.so;

# configuration file /etc/nginx/modules-enabled/50-mod-http-geoip.conf:
load_module modules/ngx_http_geoip_module.so;

# configuration file /etc/nginx/modules-enabled/50-mod-http-geoip2.conf:
load_module modules/ngx_http_geoip2_module.so;

# configuration file /etc/nginx/modules-enabled/50-mod-http-headers-more-filter.conf:
load_module modules/ngx_http_headers_more_filter_module.so;

# configuration file /etc/nginx/modules-enabled/50-mod-http-image-filter.conf:
load_module modules/ngx_http_image_filter_module.so;

# configuration file /etc/nginx/modules-enabled/50-mod-http-perl.conf:
load_module modules/ngx_http_perl_module.so;

# configuration file /etc/nginx/modules-enabled/50-mod-http-subs-filter.conf:
load_module modules/ngx_http_subs_filter_module.so;

# configuration file /etc/nginx/modules-enabled/50-mod-http-uploadprogress.conf:
load_module modules/ngx_http_uploadprogress_module.so;

# configuration file /etc/nginx/modules-enabled/50-mod-http-upstream-fair.conf:
load_module modules/ngx_http_upstream_fair_module.so;

# configuration file /etc/nginx/modules-enabled/50-mod-http-xslt-filter.conf:
load_module modules/ngx_http_xslt_filter_module.so;

# configuration file /etc/nginx/modules-enabled/50-mod-mail.conf:
load_module modules/ngx_mail_module.so;

# configuration file /etc/nginx/modules-enabled/50-mod-nchan.conf:
load_module modules/ngx_nchan_module.so;

# configuration file /etc/nginx/modules-enabled/50-mod-stream.conf:
load_module modules/ngx_stream_module.so;

# configuration file /etc/nginx/modules-enabled/70-mod-stream-geoip.conf:
load_module modules/ngx_stream_geoip_module.so;

# configuration file /etc/nginx/modules-enabled/70-mod-stream-geoip2.conf:
load_module modules/ngx_stream_geoip2_module.so;

# configuration file /etc/nginx/mime.types:

types {
    text/html                             html htm shtml;
    text/css                              css;
    text/xml                              xml;
    image/gif                             gif;
    image/jpeg                            jpeg jpg;
    application/javascript                js;
    application/atom+xml                  atom;
    application/rss+xml                   rss;

    text/mathml                           mml;
    text/plain                            txt;
    text/vnd.sun.j2me.app-descriptor      jad;
    text/vnd.wap.wml                      wml;
    text/x-component                      htc;

    image/png                             png;
    image/tiff                            tif tiff;
    image/vnd.wap.wbmp                    wbmp;
    image/x-icon                          ico;
    image/x-jng                           jng;
    image/x-ms-bmp                        bmp;
    image/svg+xml                         svg svgz;
    image/webp                            webp;

    application/font-woff                 woff;
    application/java-archive              jar war ear;
    application/json                      json;
    application/mac-binhex40              hqx;
    application/msword                    doc;
    application/pdf                       pdf;
    application/postscript                ps eps ai;
    application/rtf                       rtf;
    application/vnd.apple.mpegurl         m3u8;
    application/vnd.ms-excel              xls;
    application/vnd.ms-fontobject         eot;
    application/vnd.ms-powerpoint         ppt;
    application/vnd.wap.wmlc              wmlc;
    application/vnd.google-earth.kml+xml  kml;
    application/vnd.google-earth.kmz      kmz;
    application/x-7z-compressed           7z;
    application/x-cocoa                   cco;
    application/x-java-archive-diff       jardiff;
    application/x-java-jnlp-file          jnlp;
    application/x-makeself                run;
    application/x-perl                    pl pm;
    application/x-pilot                   prc pdb;
    application/x-rar-compressed          rar;
    application/x-redhat-package-manager  rpm;
    application/x-sea                     sea;
    application/x-shockwave-flash         swf;
    application/x-stuffit                 sit;
    application/x-tcl                     tcl tk;
    application/x-x509-ca-cert            der pem crt;
    application/x-xpinstall               xpi;
    application/xhtml+xml                 xhtml;
    application/xspf+xml                  xspf;
    application/zip                       zip;

    application/octet-stream              bin exe dll;
    application/octet-stream              deb;
    application/octet-stream              dmg;
    application/octet-stream              iso img;
    application/octet-stream              msi msp msm;

    application/vnd.openxmlformats-officedocument.wordprocessingml.document    docx;
    application/vnd.openxmlformats-officedocument.spreadsheetml.sheet          xlsx;
    application/vnd.openxmlformats-officedocument.presentationml.presentation  pptx;

    audio/midi                            mid midi kar;
    audio/mpeg                            mp3;
    audio/ogg                             ogg;
    audio/x-m4a                           m4a;
    audio/x-realaudio                     ra;

    video/3gpp                            3gpp 3gp;
    video/mp2t                            ts;
    video/mp4                             mp4;
    video/mpeg                            mpeg mpg;
    video/quicktime                       mov;
    video/webm                            webm;
    video/x-flv                           flv;
    video/x-m4v                           m4v;
    video/x-mng                           mng;
    video/x-ms-asf                        asx asf;
    video/x-ms-wmv                        wmv;
    video/x-msvideo                       avi;
}

# configuration file /etc/nginx/sites-enabled/010-mysiteb:
# HTTP

server {
        server_name mysite2 mysiteb mysite3 mysiteb;
    listen 80;  
    include commons/http-location.inc;
}

# BALANCED HAPROXY2 - TCP 81

server {
        server_name mysiteb;
    listen 443 ssl;
    ssl_certificate /etc/letsencrypt/live/mysiteb/fullchain.pem;
    ssl_certificate_key /etc/letsencrypt/live/mysiteb/privkey.pem;
    include commons/ha-location-2.inc;
}

# BALANCED HAPROXY WEB - TCP 82

server {
        server_name mysite3 mysiteb;
    listen 443 ssl;
        ssl_certificate /etc/letsencrypt/live/mysite3/fullchain.pem;
        ssl_certificate_key /etc/letsencrypt/live/mysite3/privkey.pem;
        include commons/ha-location-web.inc;
}

server {
        server_name mysite2;
        listen 443 ssl;
        ssl_certificate /etc/letsencrypt/live/mysite2/fullchain.pem;
        ssl_certificate_key /etc/letsencrypt/live/mysite2/privkey.pem;
        include commons/ha-location-web.inc;
}

# configuration file /etc/nginx/commons/http-location.inc:
        location /.well-known {
                alias /var/www/html/.well-known;
        }
        location / {
                return 301 https://$host$request_uri;
        }

# configuration file /etc/nginx/commons/ha-location-2.inc:
        location / {
                proxy_pass http://127.0.0.1:81;
                proxy_set_header Host $host;
                proxy_set_header X-Forwarded-For $remote_addr;
                proxy_set_header X-Forwarded-Host $http_host;
                proxy_set_header X-Forwarded-SSL on;
        proxy_set_header X-Forwarded-Proto https;
                error_page 502 /502error.html;
        }
        location /ws {
                proxy_pass http://127.0.0.1:81;
                proxy_http_version 1.1;
                proxy_set_header Upgrade $http_upgrade;
                proxy_set_header Connection "Upgrade";
                proxy_set_header Host $host;
                proxy_set_header X-Forwarded-For $remote_addr;
                proxy_set_header X-Forwarded-Host $http_host;
                proxy_set_header X-Forwarded-SSL on;
        proxy_set_header X-Forwarded-Proto https;
                proxy_read_timeout 120;
        }
        location = /502error.html {
                root   /usr/share/nginx/html;
                internal;
        }

# configuration file /etc/nginx/commons/ha-location-web.inc:
        location / {
                proxy_pass http://127.0.0.1:82;
                proxy_set_header Host $host;
                proxy_set_header X-Forwarded-For $remote_addr;
                proxy_set_header X-Forwarded-Host $http_host;
                proxy_set_header X-Forwarded-SSL on;
        proxy_set_header X-Forwarded-Proto https;
                error_page 502 /502error.html;
        proxy_cache mycache;
        add_header X-Cache-Status $upstream_cache_status;
        }
        location = /502error.html {
                root   /usr/share/nginx/html;
                internal;
        }

# configuration file /etc/nginx/commons/srvap1-location.inc:
        location / {
                proxy_pass http://srvap1/;
                proxy_set_header Host $host;
                proxy_set_header X-Forwarded-For $remote_addr;
                proxy_set_header X-Forwarded-Host $http_host;
                proxy_set_header X-Forwarded-SSL on;
        proxy_set_header X-Forwarded-Proto https;
                error_page 502 /502error.html;
        }
        location /ws {
                proxy_pass http://srvap1;
                proxy_http_version 1.1;
                proxy_set_header Upgrade $http_upgrade;
                proxy_set_header Connection "Upgrade";
                proxy_set_header Host $host;
                proxy_set_header X-Forwarded-For $remote_addr;
                proxy_set_header X-Forwarded-Host $http_host;
                proxy_set_header X-Forwarded-SSL on;
        proxy_set_header X-Forwarded-Proto https;
                proxy_read_timeout 120;
        }
        location = /502error.html {
                root   /usr/share/nginx/html;
                internal;
        }

# configuration file /etc/nginx/commons/srvap2-location.inc:
        location / {
                proxy_pass http://srvap2/;
                proxy_set_header Host $host;
                proxy_set_header X-Forwarded-For $remote_addr;
                proxy_set_header X-Forwarded-Host $http_host;
                proxy_set_header X-Forwarded-SSL on;
        proxy_set_header X-Forwarded-Proto https;
                error_page 502 /502error.html;
        }
        location /ws {
                proxy_pass http://srvap2;
                proxy_http_version 1.1;
                proxy_set_header Upgrade $http_upgrade;
                proxy_set_header Connection "Upgrade";
                proxy_set_header Host $host;
                proxy_set_header X-Forwarded-For $remote_addr;
                proxy_set_header X-Forwarded-Host $http_host;
                proxy_set_header X-Forwarded-SSL on;
        proxy_set_header X-Forwarded-Proto https;
                proxy_read_timeout 120;
        }
        location = /502error.html {
                root   /usr/share/nginx/html;
                internal;
        }

# configuration file /etc/nginx/sites-enabled/030-mysitea:
# HTTP

server {
        server_name mysite1 mysite4 mysite5;
    listen 80;  
    include commons/http-location.inc;
}

# BALANCED HAPROXY - TCP 81

server {
        server_name mysite4;
    listen 443 ssl;
    ssl_certificate /etc/letsencrypt/live/mysite4/fullchain.pem;
    ssl_certificate_key /etc/letsencrypt/live/mysite4/privkey.pem;
    include commons/ha-location-2.inc;
}

server {
        server_name mysite5 mysitea;
    listen 443 ssl;
        ssl_certificate /etc/letsencrypt/live/mysite5/fullchain.pem;
        ssl_certificate_key /etc/letsencrypt/live/mysite5/privkey.pem;
        include commons/ha-location-web.inc;
}

server {
        server_name mysite1;
        listen 443 ssl;
        ssl_certificate /etc/letsencrypt/live/mysite1/fullchain.pem;
        ssl_certificate_key /etc/letsencrypt/live/mysite1/privkey.pem;
        include commons/ha-location-web.inc;
}

# AP1 - TCP 10001

server {
        server_name mysite4;
        listen 10001 ssl;
        ssl_certificate /etc/letsencrypt/live/mysite4/fullchain.pem;
        ssl_certificate_key /etc/letsencrypt/live/mysite4/privkey.pem;
    include commons/srvap1-location.inc;
}

server {
        server_name mysite5 mysitea;
        listen 10001 ssl;
        ssl_certificate /etc/letsencrypt/live/mysite5/fullchain.pem;
        ssl_certificate_key /etc/letsencrypt/live/mysite5/privkey.pem;
        include commons/srvap1-location.inc;
}

server {
        server_name mysite1;
        listen 10001 ssl;
        ssl_certificate /etc/letsencrypt/live/mysite1/fullchain.pem;
        ssl_certificate_key /etc/letsencrypt/live/mysite1/privkey.pem;
        include commons/srvap1-location.inc;
}

# AP2 - TCP 10002

server {
        server_name mysite4;
        listen 10002 ssl;
        ssl_certificate /etc/letsencrypt/live/mysite4/fullchain.pem;
        ssl_certificate_key /etc/letsencrypt/live/mysite4/privkey.pem;
        include commons/srvap2-location.inc;
}

server {
        server_name mysite5 mysitea;
        listen 10002 ssl;
        ssl_certificate /etc/letsencrypt/live/mysite5/fullchain.pem;
        ssl_certificate_key /etc/letsencrypt/live/mysite5/privkey.pem;
        include commons/srvap2-location.inc;
}

server {
        server_name mysite1;
        listen 10002 ssl;
        ssl_certificate /etc/letsencrypt/live/mysite1/fullchain.pem;
        ssl_certificate_key /etc/letsencrypt/live/mysite1/privkey.pem;
        include commons/srvap2-location.inc;
}


# configuration file /etc/nginx/sites-enabled/default:
##
# You should look at the following URL's in order to grasp a solid understanding
# of Nginx configuration files in order to fully unleash the power of Nginx.
# https://www.nginx.com/resources/wiki/start/
# https://www.nginx.com/resources/wiki/start/topics/tutorials/config_pitfalls/
# https://wiki.debian.org/Nginx/DirectoryStructure
#
# In most cases, administrators will remove this file from sites-enabled/ and
# leave it as reference inside of sites-available where it will continue to be
# updated by the nginx packaging team.
#
# This file will automatically load configuration files provided by other
# applications, such as Drupal or Wordpress. These applications will be made
# available underneath a path with that package name, such as /drupal8.
#
# Please see /usr/share/doc/nginx-doc/examples/ for more detailed examples.
##

# Default server configuration
#
server {
    listen 80 default_server;
    listen [::]:80 default_server;

    # SSL configuration
    #
    # listen 443 ssl default_server;
    # listen [::]:443 ssl default_server;
    #
    # Note: You should disable gzip for SSL traffic.
    # See: https://bugs.debian.org/773332
    #
    # Read up on ssl_ciphers to ensure a secure configuration.
    # See: https://bugs.debian.org/765782
    #
    # Self signed certs generated by the ssl-cert package
    # Don't use them in a production server!
    #
    # include snippets/snakeoil.conf;

    root /var/www/html;

    # Add index.php to the list if you are using PHP
    index index.html index.htm index.nginx-debian.html;

    server_name _;

    location / {
        # First attempt to serve request as file, then
        # as directory, then fall back to displaying a 404.
        try_files $uri $uri/ =404;
    }

}
server {

    listen 127.0.0.1:1935;

    root /var/www/html;

    location / {
        stub_status;
    }

}