how do I modify instance configurations and install applications - Elastic Compute Service

You can use Cloud Assistant to compile commands used to modify configurations or install applications and run the commands on multiple Elastic Compute Service (ECS) instances at the same time. This eliminates the need to log on to instances one by one and helps save time. In this topic, shell commands for Linux are used to describe how to modify instance configurations.

Background information

Before you view the system configurations of ECS instances, make sure that you are familiar with Cloud Assistant and how to use Cloud Assistant. For more information, see Overview and Use Cloud Assistant.
The operating systems and system configurations of ECS instances determine whether the sample commands described in this topic can run on the instance. We recommend that you modify the command content based on your business requirements. You can include custom parameters {{key}} in commands to increase the applicability of the commands.
Note
The execution status and results of Cloud Assistant commands may vary based on the operating systems and system configurations of ECS instances. You can view the error messages in the execution results and troubleshoot the issues in the ECS console or by calling an API operation. For more information, see Check execution results and troubleshoot common issues.

Modify instance configurations

Scenario: Use Cloud Assistant to modify the configurations of ECS instances.
Procedure
1. Create a Cloud Assistant command and run the command on an ECS instance.
  For more information, see Create a command and Run a command.
  You can run the following sample Cloud Assistant command to add, delete, and modify user information. In this example, the useradd -m -p test** student command is run to add a user.
```
# Add a user and configure a password for the user. {{password}} is the key of a custom parameter. You must specify a value for the key before you run the command.
useradd -m -p {{password}} {{newUser}}
# Change the password.
passwd {{password}}
# Delete the user.
userdel {{newUser}}
# Modify the username.
usermod -l {{newUser}} -d /home/{{newUser}} -m {{previousUser}}
```
2. Connect to the instance.
  For more information, see Connect to a Linux instance by using a password or key.
3. On the instance logon page, view the added user.
```
[root@EcsHost ~]# su - student -c pwd
/home/student
```

Install applications

Scenario: Use Cloud Assistant to install applications on multiple ECS instances at the same time. This reduces repeated installation and deployment operations.

Procedure

Create a Cloud Assistant command and then run the command on an ECS instance.

For more information, see Create a command and Run a command.

You can run the following sample Cloud Assistant command to install Python 3. Python 3 is suitable for operating systems that use YUM, such as CentOS:

yum install zlib zlib-devel readline-devel sqlite-devel bzip2-devel openssl-devel gdbm-devel libdbi-devel ncurses-libs kernel-devel libxslt-devel libffi-devel python-devel zlib-devel openldap-devel sshpass gcc git -y
wget -c https://www.python.org/ftp/python/3.6.6/Python-3.6.6.tgz
tar -xzvf Python-3.6.6.tgz
cd Python-3.6.6
./configure --prefix=/usr/local/python3
make all
make install
make clean
make distclean  
ln -s /usr/local/python3/bin/python3 /usr/bin/python3
ln -s /usr/local/python3/bin/pip3 /usr/bin/pip3

Connect to the instance.
For more information, see Connect to a Linux instance by using a password or key.
On the instance logon page, run the python3 command to check whether Python 3 is installed.
- The following command output indicates that Python 3 is installed:
```
[root@EcsHost ~]# python3
Python 3.6.6 (default, Jan 10 20**, 14:09:05)
[GCC 4.8.5 20150623 (Red Hat 4.8.5-39)] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>>
```
- If the command not found error message is returned, Python 3 is not installed.

Upgrade applications

Scenario: Use Cloud Assistant to upgrade applications on ECS instances.
Procedure
1. Create a Cloud Assistant command and then run the command on an ECS instance.
  For more information, see Create a command and Run a command.
  You can run the following sample Cloud Assistant command to upgrade Python from 3.6.0 to 3.7.0:
```
wget https://www.python.org/ftp/python/3.7.0/Python-3.7.0.tgz && rm -rf /usr/bin/python3
tar -xzvf Python-3.7.0.tgz
cd Python-3.7.0
./configure && make && make install
ln -s /usr/local/bin/python3.7 /usr/bin/python3
ln -s /usr/local/bin/python3.7-config /usr/bin/python-config
python3 -V
```
2. Connect to the instance.
  For more information, see Connect to a Linux instance by using a password or key.
3. On the instance logon page, run the python3 -V command to check whether the application is upgraded.
```
[root@EcsHost ~]# python3 -V
Python 3.7.0
```