Nginx + rails + unicorn環境で、railsルーティングで指定したindex.htmlが表示されない

Question

自作アプリをAWSのEC2でデプロイしようとしています。
EC2インスタンスには独自ドメイン(www.example.com) を割り当てています。
http://www.example.comにアクセスすると、このページは動作していませんとエラーが出ます。
http://www.example.com/index.htmlにアクセスすると、Welcome to nginx on Amazon Linux!のページが表示され、また/var/www/projects/rails_app/publicに適当にindex.htmlを作成すると、そのページがhttp://www.example.comに表示されます。
rails_app/app/view/static_pages/index.htmlをルートに表示するにはどのように設定すればいいのでしょうか。

$ curl -I -L http://www.example.com
HTTP/1.1 301 Moved Permanently
Server: awselb/2.0
Date: Sat, 11 Apr 2020 11:32:03 GMT
Content-Type: text/html
Content-Length: 150
Connection: keep-alive
Location: https://www.example.com:443/

HTTP/2 204 
date: Sat, 11 Apr 2020 11:32:03 GMT
server: nginx/1.16.1
x-frame-options: SAMEORIGIN
x-xss-protection: 1; mode=block
x-content-type-options: nosniff
x-download-options: noopen
x-permitted-cross-domain-policies: none
referrer-policy: strict-origin-when-cross-origin
cache-control: no-cache
x-request-id: 46232335-ee08-4e5a-8371-d5cef433a33c
x-runtime: 0.001718
strict-transport-security: max-age=31536000; includeSubDomains

以下/etc/nginx/conf.d/rails_app.conf

#log directory
error_log  /var/www/projects/rails_app/log/nginx.error.log;
access_log /var/www/projects/rails_app/nginx.access.log;
#max body size
client_max_body_size 2G;
upstream app_server {
  # for UNIX domain socket setups
  server unix:/var/www/projects/rails_app/tmp/sockets/.unicorn.sock fail_timeout=0;
}
server {
  listen 80;
  server_name www.example.com;
  # nginx so increasing this is generally safe...
  keepalive_timeout 5;
  # path for static files
  root /var/www/projects/rails_app/public;
  # page cache loading
  try_files $uri/index.html $uri.html $uri @app;
  location @app {
    # HTTP headers
    proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
    proxy_set_header Host $http_host;
    proxy_redirect off;
    proxy_no_cache true;
    proxy_pass http://app_server;
  }
  # Rails error pages
  error_page 500 502 503 504 /500.html;
  location = /500.html {
    root /var/www/projects/rails_app/public;
  }
}

以下/etc/nginx/nginx.conf

# For more information on configuration, see:
#   * Official English Documentation: http://nginx.org/en/docs/
#   * Official Russian Documentation: http://nginx.org/ru/docs/

user nginx;
worker_processes auto;
error_log /var/log/nginx/error.log;
pid /run/nginx.pid;

# Load dynamic modules. See /usr/share/doc/nginx/README.dynamic.
include /usr/share/nginx/modules/*.conf;

events {
    worker_connections 1024;
}

http {
    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;
    tcp_nodelay         on;
    keepalive_timeout   65;
    types_hash_max_size 2048;

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

    # Load modular configuration files from the /etc/nginx/conf.d directory.
    # See http://nginx.org/en/docs/ngx_core_module.html#include
    # for more information.
    include /etc/nginx/conf.d/*.conf;

    server {
        listen       80 default_server;
        listen       [::]:80 default_server;
        server_name  _;
        root         /usr/share/nginx/html;

        # Load configuration files for the default server block.
        include /etc/nginx/default.d/*.conf;

        location / {
        }

        error_page 404 /404.html;
            location = /40x.html {
        }

        error_page 500 502 503 504 /50x.html;
            location = /50x.html {
        }
    }

以下unicornの設定ファイル

# set lets
$worker  = 2
$timeout = 30
$app_dir = "/var/www/projects/rails_app"
$listen  = File.expand_path 'tmp/sockets/.unicorn.sock', $app_dir
$pid     = File.expand_path 'tmp/pids/unicorn.pid', $app_dir
$std_log = File.expand_path 'log/unicorn.log', $app_dir
# set config
worker_processes  $worker
working_directory $app_dir
stderr_path $std_log
stdout_path $std_log
timeout $timeout
listen  $listen
pid $pid
# loading booster
preload_app true
# before starting processes
before_fork do |server, worker|
  defined?(ActiveRecord::Base) and ActiveRecord::Base.connection.disconnect!
  old_pid = "#{server.config[:pid]}.oldbin"
  if old_pid != server.pid
    begin
      Process.kill "QUIT", File.read(old_pid).to_i
    rescue Errno::ENOENT, Errno::ESRCH
    end
  end
end
# after finishing processes
after_fork do |server, worker|
  defined?(ActiveRecord::Base) and ActiveRecord::Base.establish_connection
end

表示したいページのルーティング
routes.rb

Rails.application.routes.draw do
  root to: 'static_pages#home'
end

#その他の環境
ドメインはroute53で取得、AWS Certificate Managerで証明書発行済
ロードバランサーALBを設定中