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Consider to insert one white space before and after English word in Japanese. Run the following script by changing a string 'YOUR_FILENAME'. The script copy the original file as YOUR_FILENAME.org and overwrite and replace the original file by inserting one white space before and after an English word. It is useful multi-byte language such as CJK (Chinese, Japanese and Korean).
export FILENAME='index.rst'; \
cp ${FILENAME} ${FILENAME}.org; \
cat ${FILENAME}.org | sed y/０１２３４５６７８９/0123456789/ | \

I think we should doubt cache since Drupal 8 aggressively uses cache-backend mechanism. If you encounter a fatal error or WSOD (White Screen of Death), check the following items.

Check error logs at /var/log/apache2/error.log

sudo tail -f /var/log/apache2/error.log

Configuration | Performance - Check off Aggregate CSS files and Aggregate JavaScript files

Configuration | Performance - Clear all caches

Rebuild cache from Drush

# Move to the directory where Drupal 8 is installed by using cd command,
sudo drush -l <YOUR_SITE_URL> cr

GRANT USAGE ON `<DATABASE_NAME>`.* TO '<USERNAME>'@'%';
GRANT ALL PRIVILEGES ON `<DATABASE_NAME>`.* TO '<USERNAME>'@'%' WITH GRANT OPTION;

1. Adjust the time amongst the server in your system
ntpdate time.apple.com

2. Check and monitor your disk space

Your service may stop after one year from the beginning of your service release date because the log files occupies a server disk space.
Use logrotate to truncate the log files (even if you are practicing that, the logs will overflow at the server).
Monitor the remaining disk space by using df command.

df -h

There are a couple of options to add a user to group(s) in Linux. The commands are gpasswd, usermod and adduser.
I recommend to use gpasswd to add a user to group, which is no harm.
gpasswd -a <USERNAME> <GROUPNAME>

You must use usermod command as follows:
usermod -aG <GROUPNAME> <USERNAME>

Use a 'tag' command on docker.
docker tag <image_id> <repository_name>:<tag>

Note: You can omit the part '<tag>' and only write '<repository_name>'. The meaning of the <tag> string after colon (:) of the repository name is that you can put a different version image by changing the date or versions.
docker tag <image_id> <repository_name>

Edit /etc/crontab
vi /etc/crontab

Every end of the month
H 23 28-31 * * /usr/bin/test $( date -d '+1 day' +%d ) -eq 1 && <COMMAND>

Every last Friday of the month
0 0 * * 5 /usr/bin/test $( date +%m ) -ne $( date --date '7 day' +%m ) && <COMMAND>

These will be useful in Jenkins.
/usr/bin/test $( date -d '+1 day' +%d ) -eq 1

or
/usr/bin/test $( date +%m ) -ne $( date --date '7 day' +%m )

List volumes
sudo docker volume ls -qf dangling=true

Delete unnecessary volumes
sudo docker volume rm $(sudo docker volume ls -qf dangling=true)

Kill all Docker containers
sudo docker kill $(sudo docker ps -q)

The following commands mount a large-scale SSD volume (/dev/xvdb) onto /mnt.
sudo mkfs.ext4 /dev/xvdb
echo "/dev/xvdb /mnt auto noatime 0 0" | sudo tee -a /etc/fstab
sudo mount /mnt

Security Group
It is enough to open the port 22 at Security Group on EC2
SSH TCP 22 0.0.0.0/32

JMeter Server Configuration
cd apache-jmeter-3.0/bin
vi ./jmeter.properties

Find and modify the following two lines
server_port=10991 # Server-side port from JMeter client: JMeter Client -> JMeter Server
server.rmi.localport=40001 # Server port to access to Client via RMI: JMeter Server -> JMeter Client