nginx实现两个域名之间跳转配置

1.我有两个域名，分别是www.a.com, www.b.com，现在我想让所有www.a.com的访问地址都跳转到www.b.com，比如 https://www.a.com/sample.html 跳转到https://www.b.com/sample.html。
2.下面是我域名www.a.com的nginx配置：

server{
    listen 80;
    server_name www.a.com a.com;
    return 301 https://$server_name$request_uri;
}


server {
   listen 443 ssl http2;
   server_name a.com www.a.com;
   index  index.php index.html index.htm;
   root   /usr/share/nginx/iwwenbo;
   add_header X-Frame-Options DENY;
   add_header X-Content-Type-Options nosniff;

   ssl_certificate /etc/letsencrypt/live/a.com/fullchain.pem;
   ssl_certificate_key /etc/letsencrypt/live/a.com/privkey.pem;
   ssl_protocols TLSv1 TLSv1.1 TLSv1.2;
   ssl_ciphers EECDH+CHACHA20:EECDH+CHACHA20-draft:EECDH+AES128:RSA+AES128:EECDH+AES256:RSA+AES256:EECDH+3DES:RSA+3DES:!MD5;
   ssl_prefer_server_ciphers on;
   ssl_session_cache shared:SSL:10m;
   ssl_session_timeout 60m;

    location / {
        try_files $uri $uri/ /index.php?$args;
    }

    location ~ \.php$ {
        fastcgi_pass   127.0.0.1:9000;
        fastcgi_index  index.php;
        fastcgi_param  SCRIPT_FILENAME  $document_root/$fastcgi_script_name;
        include        fastcgi_params;
    }

}

请问如何修改能实现上述功能，将所有https://www.a.com/sample.html的地址，全部转移到https://www.b.com/sample.html。