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Developing on AWS (CLI, SDK and IAM Policies)

• Developing on AWS (CLI, SDK and IAM Policies)
  • AWS CLI Dry Runs
  • AWS CLI STS Decode Errors
  • AWS EC2 Instance Metadata
  • MFA with CLI
  • AWS SDK Overview
  • AWS Limits (Quotas)
  • Exponential Backoff (any AWS service)
  • AWS CLI Credentials Provider Chain
  • AWS Credentials Best Practices

AWS CLI Dry Runs

• Sometimes, we’d just like to make sure we have the permissions…
• But not actually run the commands!
• Some AWS CLI commands (such as EC2) can become expensive if they succeed, say if we wanted to try to create an EC2 Instance
• Some AWS CLI commands (not all) contain a –dry-run option to simulate API calls

AWS CLI STS Decode Errors

• When you run API calls and they fail, you can get a long error message
• This error message can be decoded using the STS command line:
• sts decode-authorization-message

AWS EC2 Instance Metadata

• AWS EC2 Instance Metadata is powerful but one of the least known features to developers
• It allows AWS EC2 instances to ”learn about themselves” without using an IAM Role for that purpose.
• The URL is http://169.254.169.254/latest/meta-data
• You can retrieve the IAM Role name from the metadata, but you CANNOT retrieve the IAM Policy.
• Metadata = Info about the EC2 instance
• Userdata = launch script of the EC2 instance

MFA with CLI

• To use MFA with the CLI, you must create a temporary session
• To do so, you must run the STS GetSessionToken API call

• aws sts get-session-token –serial-number arn-of-the-mfa-device –token-code code-from-token –duration-seconds 3600

  {
    "Credentials": {
      "SecretAccessKey": "secret-access-key",
      "SessionToken": "temporary-session-token",
      "Expiration": "expiration-date-time",
      "AccessKeyId": "access-key-id"
    }
  }
  

AWS SDK Overview

• What if you want to perform actions on AWS directly from your applications code ? (without using the CLI).
• You can use an SDK (software development kit) !
• Official SDKs are…
  • Java
  • .NET
  • Node.js
  • PHP
  • Python (named boto3 / botocore)
  • Go
  • Ruby
  • C++
• We have to use the AWS SDK when coding against AWS Services such as DynamoDB
• Fun fact… the AWS CLI uses the Python SDK (boto3)
• The exam expects you to know when you should use an SDK
• We’ll practice the AWS SDK when we get to the Lambda functions
• Good to know: if you don’t specify or configure a default region, then us-east-1 will be chosen by default

AWS Limits (Quotas)

• API Rate Limits
  • DescribeInstances API for EC2 has a limit of 100 calls per seconds
  • GetObject on S3 has a limit of 5500 GET per second per prefix • For Intermittent Errors: implement Exponential Backoff
  • For Consistent Errors: request an API throttling limit increase
• Service Quotas (Service Limits)
  • Running On-Demand Standard Instances: 1152 vCPU
  • You can request a service limit increase by opening a ticket
  • You can request a service quota increase by using the Service Quotas API

Exponential Backoff (any AWS service)

• If you get ThrottlingException intermittently, use exponential backoff
• Retry mechanism already included in AWS SDK API calls
• Must implement yourself if using the AWS API as-is or in specific cases
  • Must only implement the retries on 5xx server errors and throttling
  • Do not implement on the 4xx client errors

AWS CLI Credentials Provider Chain

• The CLI will look for credentials in this order

1. Command line options – –region, –output, and –profile
2. Environment variables – AWS_ACCESS_KEY_ID, AWS_SECRET_ACCESS_KEY, and AWS_SESSION_TOKEN
3. CLI credentials file –aws configure ~/.aws/credentials on Linux / Mac & C:\Users\user.aws\credentials on Windows
4. CLI configuration file – aws configure ~/.aws/config on Linux / macOS & C:\Users\USERNAME.aws\config on Windows
5. Container credentials – for ECS tasks
6. Instance profile credentials – for EC2 Instance Profiles

AWS Credentials Best Practices

• Overall, NEVER EVER STORE AWS CREDENTIALS IN YOUR CODE
• Best practice is for credentials to be inherited from the credentials chain
• If using working within AWS, use IAM Roles
  • => EC2 Instances Roles for EC2 Instances
  • => ECS Roles for ECS tasks
  • => Lambda Roles for Lambda functions
• If working outside of AWS, use environment variables / named profiles

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