Best practice for nextcloud files failover

Hello , i have 2 linux machines that runs the same configuration for nextcloud app :

both of the servers are running the same docker compose file and Nginx configuration.

version: '3'


services:
  db:
    image: mariadb:10.6
    container_name: "mariaDB"
    command: --transaction-isolation=READ-COMMITTED --log-bin=binlog --binlog-format=ROW
    restart: always
    volumes:
      - ./db:/var/lib/mysql:Z
    environment:
      - MYSQL_ROOT_PASSWORD=PASSWORD
      - MARIADB_AUTO_UPGRADE=1
      - MARIADB_DISABLE_UPGRADE_BACKUP=1
      - MYSQL_PASSWORD=PASSWORD
      - MYSQL_DATABASE=nextcloud
      - MYSQL_USER=nextcloud

      
  redis:
    image: redis:alpine
    container_name: "redis"
    restart: always


  app:
    image: nextcloud:fpm-alpine
    container_name: "nextcloud"
    restart: always
    volumes:
      - ./nextcloud:/var/www/html:z    
    expose: 
      - "9000"
    environment:
      - MYSQL_HOST=db
      - REDIS_HOST=redis
      - MYSQL_PASSWORD=PASSWORD
      - MYSQL_DATABASE=nextcloud
      - MYSQL_USER=nextcloud
    depends_on:
      - db
      - redis


  web:
    image: nginx:alpine
    container_name: "nginx"
    restart: always
    ports:
      - 80:80
      - 443:443
    volumes:
      - ./nextcloud:/var/www/html:z,ro
      #- ./nginx.conf:/etc/nginx/nginx.conf:ro
      - ./ssl:/etc/nginx/ssl:ro
      - ./nginx.conf:/etc/nginx/nginx.conf:ro
      
      
    depends_on:
      - app

  cron:
    image: nextcloud:fpm-alpine
    container_name: "cron"
    restart: always
    volumes:
      - ./nextcloud:/var/www/html:z
    entrypoint: /cron.sh
    depends_on:
      - db
      - redis

  

nginx conf:

worker_processes auto;

error_log  /var/log/nginx/error.log warn;
pid        /var/run/nginx.pid;


events {
    worker_connections  1024;
}


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

    log_format  main  '$remote_addr - $remote_user [$time_local] "$request" '
                      '$status $body_bytes_sent "$http_referer" '
                      '"$http_user_agent" "$http_x_forwarded_for"';

    access_log  /var/log/nginx/access.log  main;

    sendfile        on;
    #tcp_nopush     on;

    # Prevent nginx HTTP Server Detection
    server_tokens   off;

    keepalive_timeout  65;

    #gzip  on;

  upstream php-handler {
    server app:9000;
    #server unix:/var/run/php/php7.4-fpm.sock;
}

# Set the `immutable` cache control options only for assets with a cache busting `v` argument
map $arg_v $asset_immutable {
    "" "";
    default "immutable";
}


  server {
    listen 80;
    
    server_name nextcloudX.domain;

    # Prevent nginx HTTP Server Detection
    server_tokens off;

    # Enforce HTTPS
    return 301 https://$server_name$request_uri;
  }

  server {
    listen 443      ssl;
    server_name nextcloudX.domain;

    # Path to the root of your installation
    root /var/www/html;

    # Use Mozilla's guidelines for SSL/TLS settings
    # https://mozilla.github.io/server-side-tls/ssl-config-generator/
    ssl_certificate     /etc/nginx/ssl/server.crt;
    ssl_certificate_key /etc/nginx/ssl/server.key;

    # Prevent nginx HTTP Server Detection
    server_tokens off;

    # HSTS settings
    # WARNING: Only add the preload option once you read about
    # the consequences in https://hstspreload.org/. This option
    # will add the domain to a hardcoded list that is shipped
    # in all major browsers and getting removed from this list
    # could take several months.
    #add_header Strict-Transport-Security "max-age=15768000; includeSubDomains; preload" always;

    # set max upload size and increase upload timeout:
    client_max_body_size 512M;
    client_body_timeout 300s;
    fastcgi_buffers 64 4K;

    # Enable gzip but do not remove ETag headers
    gzip on;
    gzip_vary on;
    gzip_comp_level 4;
    gzip_min_length 256;
    gzip_proxied expired no-cache no-store private no_last_modified no_etag auth;
    gzip_types application/atom+xml text/javascript application/javascript application/json application/ld+json application/manifest+json application/rss+xml application/vnd.geo+json application/vnd.ms-fontobject application/wasm application/x-font-ttf application/x-web-app-manifest+json application/xhtml+xml application/xml font/opentype image/bmp image/svg+xml image/x-icon text/cache-manifest text/css text/plain text/vcard text/vnd.rim.location.xloc text/vtt text/x-component text/x-cross-domain-policy;

    # Pagespeed is not supported by Nextcloud, so if your server is built
    # with the `ngx_pagespeed` module, uncomment this line to disable it.
    #pagespeed off;

    # The settings allows you to optimize the HTTP2 bandwitdth.
    # See https://blog.cloudflare.com/delivering-http-2-upload-speed-improvements/
    # for tunning hints
    client_body_buffer_size 512k;

    # HTTP response headers borrowed from Nextcloud `.htaccess`
    add_header Referrer-Policy                   "no-referrer"       always;
    add_header X-Content-Type-Options            "nosniff"           always;
    add_header X-Download-Options                "noopen"            always;
    add_header X-Frame-Options                   "SAMEORIGIN"        always;
    add_header X-Permitted-Cross-Domain-Policies "none"              always;
    add_header X-Robots-Tag                      "noindex, nofollow" always;
    add_header X-XSS-Protection                  "1; mode=block"     always;

    # Remove X-Powered-By, which is an information leak
    fastcgi_hide_header X-Powered-By;

    # Add .mjs as a file extension for javascript
    # Either include it in the default mime.types list
    # or include you can include that list explicitly and add the file extension
    # only for Nextcloud like below:
    include mime.types;
    types {
        text/javascript  mjs;
    }

    # Specify how to handle directories -- specifying `/index.php$request_uri`
    # here as the fallback means that Nginx always exhibits the desired behaviour
    # when a client requests a path that corresponds to a directory that exists
    # on the server. In particular, if that directory contains an index.php file,
    # that file is correctly served; if it doesn't, then the request is passed to
    # the front-end controller. This consistent behaviour means that we don't need
    # to specify custom rules for certain paths (e.g. images and other assets,
    # `/updater`, `/ocm-provider`, `/ocs-provider`), and thus
    # `try_files $uri $uri/ /index.php$request_uri`
    # always provides the desired behaviour.
    index index.php index.html /index.php$request_uri;

    # Rule borrowed from `.htaccess` to handle Microsoft DAV clients
    location = / {
        if ( $http_user_agent ~ ^DavClnt ) {
            return 302 /remote.php/webdav/$is_args$args;
        }
    }

    location = /robots.txt {
        allow all;
        log_not_found off;
        access_log off;
    }

    # Make a regex exception for `/.well-known` so that clients can still
    # access it despite the existence of the regex rule
    # `location ~ /(\.|autotest|...)` which would otherwise handle requests
    # for `/.well-known`.
    location ^~ /.well-known {
        # The rules in this block are an adaptation of the rules
        # in `.htaccess` that concern `/.well-known`.

        location = /.well-known/carddav { return 301 /remote.php/dav/; }
        location = /.well-known/caldav  { return 301 /remote.php/dav/; }

        location /.well-known/acme-challenge    { try_files $uri $uri/ =404; }
        location /.well-known/pki-validation    { try_files $uri $uri/ =404; }

        # Let Nextcloud's API for `/.well-known` URIs handle all other
        # requests by passing them to the front-end controller.
        return 301 /index.php$request_uri;
    }

    # Rules borrowed from `.htaccess` to hide certain paths from clients
    location ~ ^/(?:build|tests|config|lib|3rdparty|templates|data)(?:$|/)  { return 404; }
    location ~ ^/(?:\.|autotest|occ|issue|indie|db_|console)                { return 404; }

    # Ensure this block, which passes PHP files to the PHP process, is above the blocks
    # which handle static assets (as seen below). If this block is not declared first,
    # then Nginx will encounter an infinite rewriting loop when it prepends `/index.php`
    # to the URI, resulting in a HTTP 500 error response.
    location ~ \.php(?:$|/) {
        # Required for legacy support
        rewrite ^/(?!index|remote|public|cron|core\/ajax\/update|status|ocs\/v[12]|updater\/.+|oc[ms]-provider\/.+|.+\/richdocumentscode\/proxy) /index.php$request_uri;

        fastcgi_split_path_info ^(.+?\.php)(/.*)$;
        set $path_info $fastcgi_path_info;

        try_files $fastcgi_script_name =404;

        include fastcgi_params;
        fastcgi_param SCRIPT_FILENAME $document_root$fastcgi_script_name;
        fastcgi_param PATH_INFO $path_info;
        fastcgi_param HTTPS on;

        fastcgi_param modHeadersAvailable true;         # Avoid sending the security headers twice
        fastcgi_param front_controller_active true;     # Enable pretty urls
        fastcgi_pass php-handler;

        fastcgi_intercept_errors on;
        fastcgi_request_buffering off;

        fastcgi_max_temp_file_size 0;
    }

    # Serve static files
    location ~ \.(?:css|js|mjs|svg|gif|png|jpg|ico|wasm|tflite|map)$ {
        try_files $uri /index.php$request_uri;
        add_header Cache-Control "public, max-age=15778463, $asset_immutable";
        access_log off;     # Optional: Don't log access to assets

        location ~ \.wasm$ {
            default_type application/wasm;
        }
    }

    location ~ \.woff2?$ {
        try_files $uri /index.php$request_uri;
        expires 7d;         # Cache-Control policy borrowed from `.htaccess`
        access_log off;     # Optional: Don't log access to assets
    }

    # Rule borrowed from `.htaccess`
    location /remote {
        return 301 /remote.php$request_uri;
    }

    location / {
        try_files $uri $uri/ /index.php$request_uri;
    }
  }
}

for the example , i will call the nextcloud1 as the main server and nextcloud2 for backup server
both configurations are running propprly , i was able to federate the servers , share files and external mounts.

my issue now is that if nextcloud1 shared a file to nextcloud2 (i was able to see it but i didn’t open it on purpose ) and nextcloud1 went down (shutdown) when i will try to open the files in nextcloud2 i will get “Internal server error” , even after turning nextcloud1 back on , i still get this issue.

i would like to know what is the best option for me to make the files still avilable.
i was looking into db replication but then i noticed that replicating the db will not acctually help me because i want to copy the files (data) .

even if there is a solution with 3rd party application , i would like to know.

Not supported. See https://github.com/nextcloud/server/issues/8459

Also see thread at Mirroring of two nextcloud server - #3 by FriendlyGamer