2017-12-17

Distributed Parallel Fault Tolerant File System with GlusterFS 

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1. Summary

In this post, I explained “GlusterFS” as one of the source code synchronization solutions between web servers in a clustered environment.
If we use this solution, the difference in source code due to deployment time lag will not occur between web servers.
In addition, since “GlusterFS” is a distributed parallel fault tolerant file system, the effective range of this solution is not limited to Web servers.
Depending on how you use it, you can build any fault tolerant file system on a large system.


2. GlusgerFS Introduction

Are you using “rsync” or “lsyncd” for synchronzing the file system between each node in a business cluster environment?
To make the story clearer, I will explain web servers as an example, but this issue is not limited to web servers.
There are several ways to synchronize project source code between web servers in a cluster environment.
First, let's give some Bad know-how.
For example, I often hear how to synchronize to each node using a shell script with “rsync” implemented.
Even if you manually deploy to each node, the problem will be few if the system is small.
However, even if synchronization is automated using “cron” with the shortest period, source code differences will occur for up to one minute.
In addition, I sometimes hear how to automatically detect source code changes using “lsyncd” and synchronize incrementally to each node.
However, this synchronization method may take several tens of seconds at the shortest before synchronization is completed.
Furthermore, these synchronization methods are unidirectional synchronization, so there are no guarantee of data consistency.
I also hear pretty much how to automatically deploy to each node using ci tools.
However, these synchronization methods only fill the time difference between manual and automatic, which is not a fundamental solution.
If these synchronization processes are performed to each node by serial processing, there will be a time difference of “number of nodes x time difference” until synchronization is completed.
It would be better to do it at least by parallel processing.
If these statuses are not a problem in UX, data management and other aspects, this post will be useless.
If there is a problem, there are a number of these solutions.
As one of its solutions, you have a way to use “GlusterFS.”
GlusterFS is a distributed parallel fault tolerant file system.
One of the advantages of using GlusterFS is that fault-tolerant design can be realized, such as file system distribution, synchronization, capacity increase/decrease can be realized with no system stop.
Naturally, synchronization is bidirectional and there is no concept of master and slave.
However, you should not include files in this volume what will continue to be locked by the daemon.
If you do not make a mistake in usage, GlusterFS will do a great deal of power.
In this post, I will explain how to implement GlusterFS.
In this post, I will not announce actual measurements on sync speed, so you should implement and judge.


3. GlusterFS Architecture

The following figure is a rough concept of GlusterFS.




In addition, the following figure is a structure example of this post.



It does not prepare volume server cluster, it is a simple self-contained  structure.
The Web server itself is a volume server and a client, and it is a mechanism that mounts from the client and connects to its own volume.
Naturally, it is possible to change the system configuration by increasing/decreasing the brick.


4. GlusterFS Environment

CentOS-7
GlusterFS 3.12


5. GlusterFS Servers Configuration


5-1. Install GlusterFS servers

# Both Web Server 1 and 2

$ sudo yum -y install centos-release-gluster
$ sudo yum -y install glusterfs-server



5-2. Startup GlusterFS servers

# Both Web Server 1 and 2

$ sudo systemctl start glusterd
$ sudo systemctl enable glusterd
$ sudo systemctl status glusterd



5-3. Set GlusgerFS hosts name

# Both Web Server 1 and 2

$ sudo vim /etc/hosts



10.0.0.1 web1.example.com
10.0.0.2 web2.example.com



5-4. Create GlusgerFS storage pool

# Only Web Server 1

$ sudo gluster peer probe web2.example.com



5-5. Confirm GlusgerFS storage pool

# Both Web Server 1 and 2

$ gluster peer status



5-6. Create GlusterFS volume

# Only Web Server 1

$ sudo gluster volume create server replica 2 web1.example.com:/server/ web2.example.com:/server/ force



5-7. Confirm GlusgerFS volume information

# Both Web Server 1 and 2

$ sudo gluster volume info



5-8. Start GlusgerFS volume

# Only Web Server 1

$ sudo gluster volume start server



5-9. Conform GlusgerFS volume status

# Both Web Server 1 and 2

$ sudo gluster volume status




6. GlusterFS Clients Configuration


6-1. Install GlusgerFS Clients

# Both Web Server 1 and 2

$ sudo yum -y install glusterfs glusterfs-fuse glusterfs-rdma



6-2. Mount Client to Server

# Web Server 1

$ sudo mkdir /client
$ sudo mount -t glusterfs web1.example.com:/server /client
$ sudo df -Th


# Web Server 2

$ sudo mkdir /client
$ sudo mount -t glusterfs web2.example.com:/server /client
$ sudo df -Th



6-3. Auto mount GlusgerFS Server

# Web Server 1

$ sudo vim /etc/fstab



web1.example.com:/server       /client   glusterfs       defaults,_netdev        0 0

# Web Server 2

$ sudo vim /etc/fstab



web2.example.com:/server       /client   glusterfs       defaults,_netdev        0 0
o

6-4. Test GlusgerFS replication

# Web Server 1

$ sudo cd /client
$ sudo touch test.txt
$ sudo ls


# Web Server 2

$ sudo cd /client
$ sudo ls
$ sudo rm text.txt


# Web Server 1

$ sudo ls




7. GlusgerFS Conclusion

In this post, I explained “GlusterFS” as one of the source code synchronization solutions between web servers in a clustered environment.
If you use this solution, the difference in source code due to deployment time lag will not occur between web servers.
In this way, once we have the foundation of the system, we will not have to use the CI tools desperately.
In addition, since GlusterFS is a distributed parallel fault tolerant file system, the effective range of this solution is not limited to Web servers.
Depending on how you use it, you can build any fault tolerant file system on a large system.
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2017-12-13

Seconds Access Limiter for Web API with Python, PHP, Ruby, and Perl 

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1. Summary

In this article, I will describe the access limitation solution that is often required in Web APIs.
In addition, I will exemplify “One-Second Access Limiter” which is one of access limit solutions using sample codes of Python, PHP, Ruby and Perl interpreter languages.


2. Introduction

In the Web API service development project, we may be presented with requirements such as “access limitation within a certain period.”
For example, the requirement is such that the Web API returns the HTTP status code of “429 Too Many Requests” when the number of accesses is exceeded.
These designers and developers will be forced to improve the speed and reducing the load of this process.
This is because if the resource load reduction is the purpose of access limitation, it is meaningless if the logic is increasing the load.
In addition, when the reference time is short and the accuracy of the result is required, the accuracy of the algorithm is required.
If you are an engineer with the experience of developing Web Application Firewall (WAF), you should already know these things.
In the world, there are many access limitation solutions, but in this post I will provide a sample of “One-Second Access Limiter” as one of its solutions.


3. Requirements

"Access limitation up to N times per second"

1. If the access exceeds N times per second, return the HTTP status code of "429 Too Many Requests" and block accesses.

2. However, the numerical value assigned to “N” depends on the specification of the project.

3. Because of the nature of access control for 1 second, this processing should not be a bottleneck of access processing capability.


4. Key Points of Architectures

Even from the above requirements, it must be processed as fast and light as possible.


# Prohibition of Use of Web Application Framework

Even if you are using a lightweight framework, loading a framework takes a lot of load.
Therefore, this process should be implemented “before processing into the framework.”


# Libraries Loading

In order to minimize the load due to library loading, it should focus on built-in processing.


# Exception/Error Handling

Increasing the load by relying on the framework for exceptions and error handling makes no sense.
These should be implemented simply in low-level code.


# Data Resource Selection

It is better to avoid heavyweight data resources like RDBMS, but in this requirement "Eventual Consistency" is not a good idea.
Realizing with Loadbalancer or Reverse Proxy is also one solution, but the more the application layer is handled, the more the processing cost of the whole communication is incurred.
Semi-synchronization such as memory cache and lightweight NoSQL is one option, but in this paper I use file system as data resource.
In order to prevent wait processing such as file locking, it is controlled by the file name and the number of files.
However, in the case of a cluster environment, a data synchronization solution is necessary.


5. Environments

The OS of sample codes is Linux.
I prepared Python, PHP, Ruby, Perl as sample code languages.

# "Python-3" Sample Code

# "PHP-5" Sample Code

# "Ruby-2" Sample Code

# "Perl-5" Sample Code



6. "Python" Sample Code

Seconds Access Limiter with Python.
Version: Python-3

#!/usr/bin/python
# coding:utf-8

import time
import datetime
import cgi
import os
from pathlib import Path
import re
import sys
import inspect
import traceback
import json

# Definition
def limitSecondsAccess():
    try:
        # Init
        ## Access Timestamp Build
        sec_usec_timestamp = time.time()
        sec_timestamp = int(sec_usec_timestamp)

        ## Access Limit Default Value
        ### Depends on Specifications: For Example 10
        access_limit = 10

        ## Roots Build
        ### Depends on Environment: For Example '/tmp'
        tmp_root = '/tmp'
        access_root = os.path.join(tmp_root, 'access')

        ## Auth Key
        ### Depends on Specifications: For Example 'app_id'
        auth_key = 'app_id'

        ## Response Content-Type
        ### Depends on Specifications: For Example JSON and UTF-8
        response_content_type = 'Content-Type: application/json; charset=utf-8'

        ### Response Bodies Build
        ### Depends on Design
        response_bodies = {}

        # Authorized Key Check
        query = cgi.FieldStorage()
        auth_id = query.getvalue(auth_key)
        if not auth_id:
            raise Exception('Unauthorized', 401)
    
        # The Auth Root Build
        auth_root = os.path.join(access_root, auth_id)

        # The Auth Root Check
        if not os.path.isdir(auth_root):
            # The Auth Root Creation
            os.makedirs(auth_root, exist_ok=True)

        # A Access File Creation Using Micro Timestamp
        ## For example, other data resources such as memory cache or RDB transaction.
        ## In the case of this sample code, it is lightweight because it does not require file locking and transaction processing.
        ## However, in the case of a cluster configuration, file system synchronization is required.
        access_file_path = os.path.join(auth_root, str(sec_usec_timestamp))
        path = Path(access_file_path)
        path.touch()

        # The Access Counts Check
        access_counts = 0
        for base_name in os.listdir(auth_root):
            ## A Access File Path Build
            file_path = os.path.join(auth_root, base_name)

            ## Not File Type
            if not os.path.isfile(file_path):
                continue

            ## The Base Name Data Type Casting
            base_name_sec_usec_timestamp = float(base_name)
            base_name_sec_timestamp = int(base_name_sec_usec_timestamp)

            ## Same Seconds Stampstamp
            if sec_timestamp == base_name_sec_timestamp:

                ### A Overtaken Processing
                if sec_usec_timestamp < base_name_sec_usec_timestamp:
                    continue

                ### Access Counts Increment
                access_counts += 1

                ### Too Many Requests
                if access_counts > access_limit:
                    raise Exception('Too Many Requests', 429)

                continue

            ## Past Access Files Garbage Collection
            if sec_timestamp > base_name_sec_timestamp:
                os.remove(file_path)

    except Exception as e:
        # Exception Tuple to HTTP Status Code
        http_status = e.args[0]
        http_code = e.args[1]

        # 4xx
        if http_code >= 400 and http_code <= 499:
            # logging
            ## snip...
        # 5xx
        elif http_code >= 500:
            # logging
            # snip...

            ## The Exception Message to HTTP Status
            http_status = 'foo'
        else:
            # Logging
            ## snip...

            # HTTP Status Code for The Response
            http_status = 'Internal Server Error'
            http_code = 500

        # Response Headers Feed
        print('Status: ' + str(http_code) + ' ' + http_status)
        print(response_content_type + "\n\n")

        # A Response Body Build
        response_bodies['message'] = http_status
        response_body = json.dumps(response_bodies)

        # The Response Body Feed
        print(response_body)

# Excecution
limitSecondsAccess()





7. "PHP" Sample Code

Seconds Access Limiter with PHP
Version: PHP-5

<?php
# Definition
function limitSecondsAccess()
{
    try {
        # Init
        ## Access Timestamp Build
        $sec_usec_timestamp = microtime(true);
        list($sec_timestamp, $usec_timestamp) = explode('.', $sec_usec_timestamp);

        ## Access Limit Default Value
        ### Depends on Specifications: For Example 10
        $access_limit = 10;

        ## Roots Build
        ### Depends on Environment: For Example '/tmp'
        $tmp_root = '/tmp';
        $access_root = $tmp_root . '/access';

        ## Auth Key
        ### Depends on Specifications: For Example 'app_id'
        $auth_key = 'app_id';

        ## Response Content-Type
        ## Depends on Specifications: For Example JSON and UTF-8
        $response_content_type = 'Content-Type: application/json; charset=utf-8';

        ## Response Bodies Build
        ### Depends on Design
        $response_bodies = array();

        # Authorized Key Check
        if (empty($_REQUEST[$auth_key])) {
            throw new Exception('Unauthorized', 401);
        }
        $auth_id = $_REQUEST[$auth_key];

        # The Auth Root Build
        $auth_root = $access_root . '/' . $auth_id;

        # The Auth Root Check
        if (! is_dir($auth_root)) {
            ## The Auth Root Creation
            if (! mkdir($auth_root, 0775, true)) {
                throw new Exception('Could not create the auth root. ' . $auth_root, 500);
            }
        }

        # A Access File Creation Using Micro Timestamp
        /* For example, other data resources such as memory cache or RDB transaction.
         * In the case of this sample code, it is lightweight because it does not require file locking and transaction processing.
         * However, in the case of a cluster configuration, file system synchronization is required.
         */
        $access_file_path = $auth_root . '/' . strval($sec_usec_timestamp);
        if (! touch($access_file_path)) {
            throw new Exception('Could not create the access file. ' . $access_file_path, 500);
        }

        # The Auth Root Scanning
        if (! $base_names = scandir($auth_root)) {
            throw new Exception('Could not scan the auth root. ' . $auth_root, 500);
        }

        # The Access Counts Check
        $access_counts = 0;
        foreach ($base_names as $base_name) {
            ## A current or parent dir
            if ($base_name === '.' || $base_name === '..') {
                continue;
            }

            ## A Access File Path Build
            $file_path = $auth_root . '/' . $base_name;

            ## Not File Type
            if (! is_file($file_path)) {
                continue;
            }

            ## The Base Name to Integer Data Type
            $base_name_sec_timestamp = intval($base_name);

            ## Same Seconds Timestamp
            if ($sec_timestamp === $base_name_sec_timestamp) {
            
                ## The Base Name to Float Data Type
                $base_name_sec_usec_timestamp = floatval($base_name);

                ### A Overtaken Processing
                if ($sec_usec_timestamp < $base_name_sec_usec_timestamp) {
                    continue;
                }

                ### Access Counts Increment
                $access_counts++;

                ### Too Many Requests
                if ($access_counts > $access_limit) {
                    throw new Exception('Too Many Requests', 429);
                }

                continue;
            }

            ## Past Access Files Garbage Collection
            if ($sec_timestamp > $base_name_sec_timestamp) {
                @unlink($file_path);
            }
        }
    } catch (Exception $e) {
        # The Exception to HTTP Status Code
        $http_code = $e->getCode();
        $http_status = $e->getMessage();

        # 4xx
        if ($http_code >= 400 && $http_code <= 499) {
            # logging
            ## snip...
        # 5xx
        } else if ($http_code >= 500) {
            # logging
            ## snip...

            # The Exception Message to HTTP Status
            $http_status = 'foo';
        # Others
        } else {
            # Logging
            ## snip...

            # HTTP Status Code for The Response
            $http_status = 'Internal Server Error';
            $http_code = 500;
        }

        # Response Headers Feed
        header('HTTP/1.1 ' . $http_code . ' ' . $http_status);
        header($response_content_type);

        # A Response Body Build
        $response_bodies['message'] = $http_status;
        $response_body = json_encode($response_bodies);
        
        # The Response Body Feed
        exit($response_body);
    }
}

# Execution
limitSecondsAccess();
?>





8. "Ruby" Sample Code

Seconds Access Limiter with Ruby
Version: Ruby-2

# Definition#!/usr/bin/ruby
# -*- coding: utf-8 -*-

require 'time'
require 'fileutils'
require 'cgi'
require 'json'

def limitScondsAccess

    begin
        # Init
        ## Access Timestamp Build
        time = Time.now
        sec_timestamp = time.to_i
        sec_usec_timestamp_string = "%10.6f" % time.to_f
        sec_usec_timestamp = sec_usec_timestamp_string.to_f

        ## Access Limit Default Value
        ### Depends on Specifications: For Example 10
        access_limit = 10

        ## Roots Build
        ### Depends on Environment: For Example '/tmp'
        tmp_root = '/tmp'
        access_root = tmp_root + '/access'

        ## Auth Key
        ### Depends on Specifications: For Example 'app_id'
        auth_key = 'app_id'

        ## Response Content-Type
        ### Depends on Specifications: For Example JSON and UTF-8
        response_content_type = 'application/json'
        response_charset = 'utf-8'

        ## Response Bodies Build
        ### Depends on Design
        response_bodies = {}

        # Authorized Key Check
        cgi = CGI.new
        if ! cgi.has_key?(auth_key) then
            raise 'Unauthorized:401'
        end
        auth_id = cgi[auth_key]

        # The Auth Root Build
        auth_root = access_root + '/' + auth_id

        # The Auth Root Check
        if ! FileTest::directory?(auth_root) then
            # The Auth Root Creation
            if ! FileUtils.mkdir_p(auth_root, :mode => 0775) then
                raise 'Could not create the auth root. ' + auth_root + ':500'
            end
        end

        # A Access File Creation Using Micro Timestamp
        ## For example, other data resources such as memory cache or RDB transaction.
        ## In the case of this sample code, it is lightweight because it does not require file locking and transaction processing.
        ## However, in the case of a cluster configuration, file system synchronization is required.
        access_file_path = auth_root + '/' + sec_usec_timestamp.to_s
        if ! FileUtils::touch(access_file_path) then
            raise 'Could not create the access file. ' + access_file_path + ':500'
        end

        # The Access Counts Check
        access_counts = 0
        Dir.glob(auth_root + '/*') do |access_file_path|

            # Not File Type
            if ! FileTest::file?(access_file_path) then
                next
            end

            # The File Path to The Base Name
            base_name = File.basename(access_file_path)

            # The Base Name to Integer Data Type
            base_name_sec_timestamp = base_name.to_i

            # Same Seconds Timestamp
            if sec_timestamp == base_name_sec_timestamp then

                ### The Base Name to Float Data Type
                base_name_sec_usec_timestamp = base_name.to_f

                ### A Overtaken Processing
                if sec_usec_timestamp < base_name_sec_usec_timestamp then
                    next
                end

                ### Access Counts Increment
                access_counts += 1

                ### Too Many Requests
                if access_counts > access_limit then
                    raise 'Too Many Requests:429'
                end

                next
            end

            # Past Access Files Garbage Collection
            if sec_timestamp > base_name_sec_timestamp then
                File.unlink access_file_path
            end
        end

        # The Response Feed
        cgi.out({
            ## Response Headers Feed
            'type' => 'text/html',
            'charset' => response_charset,
        }) {
            ## The Response Body Feed
            ''
        }

    rescue => e
        # Exception to HTTP Status Code
        messages = e.message.split(':')
        http_status = messages[0]
        http_code = messages[1]

        # 4xx
        if http_code >= '400' && http_code <= '499' then
            # logging
            ## snip...
        # 5xx
        elsif http_code >= '500' then
            # logging
            ## snip...

            # The Exception Message to HTTP Status
            http_status = 'foo'
        else
            # Logging
            ## snip...

            # HTTP Status Code for The Response
            http_status = 'Internal Server Error'
            http_code = '500'
        end

        # The Response Body Build
        response_bodies['message'] = http_status
        response_body = JSON.generate(response_bodies)

        # The Response Feed
        cgi.out({
            ## Response Headers Feed
            'status' => http_code + ' ' + http_status,
            'type' => response_content_type,
            'charset' => response_charset,
        }) {
            ## The Response Body Feed
            response_body
        }
    end
end

limitScondsAccess





9. "Perl" Sample Code

Seconds Access Limiter with Perl
Version: Perl-5

#!/usr/bin/perl

use strict;
use warnings;
use utf8;
use Time::HiRes qw(gettimeofday);
use CGI;
use File::Basename;
use JSON;

# Definition
sub limitSecondsAccess {

    eval {
        # Init
        ## Access Timestamp Build
        my ($sec_timestamp, $usec_timestamp) = gettimeofday();
        my $sec_usec_timestamp = ($sec_timestamp . '.' . $usec_timestamp) + 0;

        ## Access Limit Default Value
        ### Depends on Specifications: For Example 10
        my $access_limit = 10;

        ## Roots Build
        ### Depends on Environment: For Example '/tmp'
        my $tmp_root = '/tmp';
        my $access_root = $tmp_root . '/access';

        ## Auth Key
        ### Depends on Specifications: For Example 'app_id'
        my $auth_key = 'app_id';

        ## Response Content-Type
        ## Depends on Specifications: For Example JSON and UTF-8

        ## Response Bodies Build
        ### Depends on Design
        my %response_bodies;

        # Authorized Key Check
        my $CGI = new CGI;
        if (! defined($CGI->param($auth_key))) {
            die('Unauthorized`401`');
        }
        my $auth_id = $CGI->param($auth_key);

        # The Auth Root Build
        my $auth_root = $access_root . '/' . $auth_id;

        # The Access Root Check
        if (! -d $access_root) {
            ## The Access Root Creation
            if (! mkdir($access_root)) {
                die('Could not create the access root. ' . $access_root . '`500`');
            }
        }

        # The Auth Root Check
        if (! -d $auth_root) {
            ## The Auth Root Creation
            if (! mkdir($auth_root)) {
                die('Could not create the auth root. ' . $auth_root . '`500`');
            }
        }

        # A Access File Creation Using Micro Timestamp
        ## For example, other data resources such as memory cache or RDB transaction.
        ## In the case of this sample code, it is lightweight because it does not require file locking and transaction processing.
        ## However, in the case of a cluster configuration, file system synchronization is required.
        my $access_file_path = $auth_root . '/' . $sec_usec_timestamp;
        if (! open(FH, '>', $access_file_path)) {
            close FH;
            die('Could not create the access file. ' . $access_file_path . '`500`');
        }
        close FH;

        # The Auth Root Scanning
        my @file_pathes = glob($auth_root . "/*");
        if (! @file_pathes) {
            die('Could not scan the auth root. ' . $auth_root . '`500`');
        }

        # The Access Counts Check
        my $access_counts = 0;
        foreach my $file_path (@file_pathes) {

            ## Not File Type
            if (! -f $file_path) {
                next;
            }

            ## The Base Name Extract
            my $base_name = basename($file_path);

            ## The Base Name to Integer Data Type
            my $base_name_sec_timestamp = int($base_name);

            ## Same Seconds Timestamp
            if ($sec_timestamp eq $base_name_sec_timestamp) {
            
                ## The Base Name to Float Data Type
                my $base_name_sec_usec_timestamp = $base_name;

                ### A Overtaken Processing
                if ($sec_usec_timestamp lt $base_name_sec_usec_timestamp) {
                    next;
                }

                ### Access Counts Increment
                $access_counts++;

                ### Too Many Requests
                if ($access_counts > $access_limit) {
                    die("Too Many Requests`429`");
                }

                next;
            }

            ## Past Access Files Garbage Collection
            if ($sec_timestamp gt $base_name_sec_timestamp) {
                unlink($file_path);
            }
        }
    };

    if ($@) {
        # Error Elements Extract
        my @e = split(/`/, $@);

        # Exception to HTTP Status Code
        my $http_status = $e[0];
        my $http_code = '0';
        if (defined($e[1])) {
            $http_code = $e[1];
        }

        # 4xx
        if ($http_code ge '400' && $http_code le '499') {
            # logging
            ## snip...
        # 5xx
        } elsif ($http_code ge '500') {
            # logging
            ## snip...

            ## The Exception Message to HTTP Status
            $http_status = 'foo';
        # Others
        } else {
            # logging
            ## snip...

            $http_status = 'Internal Server Error';
            $http_code = '500';
        }

        # Response Headers Feed
        print("Status: " . $http_code . " " . $http_status . "\n");
        print('Content-Type: application/json; charset=utf-8' . "\n\n");

        # A Response Body Build
        my %response_bodies;
        $response_bodies{'message'} = $http_status;
        $a = \%response_bodies;
        my $response_body = encode_json($a);

        # The Response Body Feed
        print($response_body);
    }

}

# #Excecution
&limitSecondsAccess();




10. Conclusion

In this post, I exemplified a sample of “One-Second Access limiter” solution using Python, PHP, Ruby and Perl interpreter languages.
Because of the nature of “access control for one second”, it will be understood that low load, high speed processing and data consistency are required.
Therefore, although there are some important points, they are as described in the architecture section.
In this post, I showed a solution using file name and file number of file system.
However, in a clustered environment, it is unsuitable for this architecture if the selected data synchronization solution is slow.
In such cases, the asynchronous data architecture may be one of the options rather.
In such a case, control is made on a per-node basis.
Furthermore, the importance of the load balancing threshold is increased, and the precision of the access limitation and consistency of the result must be abandoned.
However, unless precision of access limitation and consistency of results are required, it is also one.
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