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Pablo Rodriguez

Other Ec2 Config

Other EC2 Configuration Considerations

Section titled “Other EC2 Configuration Considerations”

EC2 Instance User Data

Section titled “EC2 Instance User Data”

When you launch an EC2 instance, you can specify user data to run an initialization script (shell script or cloud-init directive):

Key Characteristics:

Section titled “Key Characteristics:”
  • Execution timing: Runs with root or Administrator privileges after instance starts, but before it’s accessible on the network
  • Implementation: Script containing shell commands or cloud-init directives
  • Purpose: Initialize the instance with custom configurations

Common User Data Tasks:

Section titled “Common User Data Tasks:”
  • Update all packages installed on the instance
  • Start installed services (e.g., Apache HTTP web server)
  • Configure services to automatically start when instance boots
  • Install additional software
  • Fetch and install software license keys
  • Patch and update software from the AMI

User Data Logs:

Section titled “User Data Logs:”
  • Linux instances: /var/log/cloud-init-output.log
  • Windows instances: C:\ProgramData\Amazon\EC2-Windows\Launch\Log\UserdataExecution.log

Retrieving Instance Metadata

Section titled “Retrieving Instance Metadata”

Instance metadata is information about your instance accessible from the instance at:

URL http://169.254.169.254/latest/meta-data/

Available Metadata Examples:

Section titled “Available Metadata Examples:”
MetadataValue
instance-idi-1234567890abcdef0
mac00-1B-63-84-45-E6
public-hostnameec2-203-0-113-25.compute-1.amazonaws.com
public-ipv467.202.51.223
local-ipv410.251.50.12

Working with User Data on Running Instances

Section titled “Working with User Data on Running Instances”
  1. Stop the instance Current user data example:
    original-userdata.sh
    #!/bin/bash
    yum update -y
  2. Modify the user data script Modified user data example:
    modified-userdata.sh
    #!/bin/bash
    yum update -y
    yum install httpd
    service httpd start
    chkconfig httpd on
  3. Remove the config_scripts_user file Command to remove config_scripts_user file:
    remove-sem.sh
    sudo rm /var/lib/cloud/instances/*/sem/config_scripts_user
  4. Re-run the user data script Options:
    • Restart the instance (user data runs automatically)
    • Run command without restarting:
    run-userdata.sh
    /var/lib/cloud/instance/scripts/part-001

Critical If you skip step 3, your modified user data script won’t run.

Manually Running Commands Best Practices

Section titled “Manually Running Commands Best Practices”

Best Practices

Web server A approach:

  • Launch with user data script
  • Run additional commands manually
  • Update user data script to retain configuration record
  • Can copy user data to new instances with same configurations

Not Best Practices

Web server B approach:

  • Launch with user data script
  • Run additional commands manually
  • Don’t update user data script
  • Cannot replicate full configuration when copying user data

Benefits of Updating User Data:

Section titled “Benefits of Updating User Data:”
  • Maintain a record of the configuration for the instance (version control)
  • Copy user data from one instance to new instances requiring same configurations

AMI Deployment Models

Section titled “AMI Deployment Models”

Base AMIs:

  • AMIs configured with OS-only
  • Fully configurable and upgradeable
  • Shorter build time
  • Slower boot time

Used as base AMI from which to create silver or golden AMIs

The model you choose impacts how these configurations are provisioned:

  • Security updates
  • New versions of your applications
  • Application configuration changes
  • Updates to dependencies

Placement Groups

Section titled “Placement Groups”

Placement groups give you control of where a group of interdependent instances run in an Availability Zone:

Placement Benefits:

Section titled “Placement Benefits:”
  • Increase network performance between instances
  • Reduce correlated or simultaneous failure

Placement Limitations:

Section titled “Placement Limitations:”
  • An instance can be launched in only one placement group at a time
  • Instances with a tenancy of host can’t be launched in a placement group

Placement Strategies:

Section titled “Placement Strategies:”

Cluster

Packs instances close together inside an Availability Zone

Benefits: Helps workloads achieve low-latency network performance

Partition

Spreads instances across logical partitions

Benefits: Groups of instances in one partition do not share underlying hardware with groups in different partitions

Spread

Strictly places small group of instances across distinct underlying hardware

Benefits: Reduces correlated failures

User data lets you configure an EC2 instance when you launch it. Information about a running instance can be accessed through an instance metadata URL. There are three main AMI deployment models: Basic AMIs, Silver AMIs and Golden AMIs. Placement groups give you control of where a group of interdependent instances run in an Availability Zone.