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aws-curl

aws-curl is like curl but with automatic SIGV4 signing to simplify calling AWS services without requirement to have AWS CLI and Python to be installed.

The script is pure shell script designed for embedded and lightweight linux distributions, docker images etc.

This utility also takes much less RAM than aws cli, so nano ec2 instances are not dying with "Out of memory" when trying to download from s3 as aws cli does.

Prerequisites

Dependencies:

  • openssl (or libressl)
  • curl
  • GNU or similar coreutils (date/od/paste)
  • GNU or similar sed

GNU coreutils/sed can be installed on macOS using Homebrew: brew install coreutils gsed

On OpenWRT you might need to install at least coreutils-od and coreutils-paste to get it working.

Installation

curl -s https://raw.githubusercontent.com/sormy/aws-curl/master/aws-curl -o /usr/local/bin/aws-curl
chmod +x /usr/local/bin/aws-curl

AWS credentials

Before you can use the application, you need to set environment variables with AWS credentials.

Set AWS credentials and region using standard AWS CLI environment variables:

  • AWS_ACCESS_KEY_ID - AWS public access key
  • AWS_SECRET_ACCESS_KEY - AWS private secret key
  • AWS_SESSION_TOKEN - temporary token received from STS or from EC2 metadata
  • AWS_DEFAULT_REGION - AWS default region, in case if region is not provided in URL or as command line argument --region.

You can read more about AWS CLI environment variables here: https://docs.aws.amazon.com/cli/latest/userguide/cli-configure-envvars.html

NOTE: Wrapper doesn't read configuration files generated by AWS CLI and reads credentials only from environment variables.

Usage

Application has the same syntax of command line arguments as curl, it just automatically adds mandatory headers to make AWS to accept the request.

AWS provides documentation for all APIs, sometimes with explicit curl usage examples. Find an API documentation you want to call and follow documentation to construct valid command line request.

Example 1: CloudWatchLogs.CreateLogGroup

Documentation: https://docs.aws.amazon.com/AmazonCloudWatchLogs/latest/APIReference/API_CreateLogGroup.html

Reference example http request:

POST / HTTP/1.1
Host: logs.<region>.<domain>
X-Amz-Date: <DATE>
Authorization: AWS4-HMAC-SHA256 Credential=<Credential>, SignedHeaders=content-type;date;host;user-agent;x-amz-date;x-amz-target;x-amzn-requestid, Signature=<Signature>
User-Agent: <UserAgentString>
Accept: application/json
Content-Type: application/x-amz-json-1.1
Content-Length: <PayloadSizeBytes>
Connection: Keep-Alive
X-Amz-Target: Logs_20140328.CreateLogGroup
{
  "logGroupName": "my-log-group"
}

The corresponding aws-curl request is:

aws-curl --request POST \
  --header "Content-Type: application/x-amz-json-1.1" \
  --header "x-amz-target: Logs_20140328.CreateLogGroup" \
  --header "Accept: application/json" \
  --data '{"logGroupName": "my-log-group"}' \
  "https://logs.us-east-1.amazonaws.com"

Example 2: STS.GetCallerIdentity

Documentation: https://docs.aws.amazon.com/STS/latest/APIReference/API_GetCallerIdentity.html

Reference example http request:

POST / HTTP/1.1
Host: sts.amazonaws.com
Accept-Encoding: identity
Content-Length: 32
Content-Type: application/x-www-form-urlencoded
Authorization: AWS4-HMAC-SHA256 Credential=AKIAI44QH8DHBEXAMPLE/20160126/us-east-1/sts/aws4_request,
        SignedHeaders=host;user-agent;x-amz-date,
        Signature=1234567890abcdef1234567890abcdef1234567890abcdef1234567890abcdef
X-Amz-Date: 20160126T215751Z
User-Agent: aws-cli/1.10.0 Python/2.7.3 Linux/3.13.0-76-generic botocore/1.3.22

Action=GetCallerIdentity&Version=2011-06-15

The corresponding aws-curl request is:

aws-curl --request POST \
  --header "Content-Type: application/x-www-form-urlencoded" \
  --data "Action=GetCallerIdentity" \
  --data "Version=2011-06-15" \
  --region "us-east-1" \
  "https://sts.amazonaws.com"

NOTE: Region can't be detected from URL, so it should be explicitly provided as argument or as AWS_DEFAULT_REGION env variable.

NOTE: This API has xml response format by default, pass Accept: application/json header to change response format.

Example 3: S3

Download file from s3 to local file:

aws-curl --request GET \
  --output "my-file.txt" \
  --region "us-east-1" \
  "https://s3.amazonaws.com/my-bucket/my-file.txt"

Download file from s3 and print to stdout:

aws-curl --request GET \
  --region "us-east-1" \
  "https://s3.amazonaws.com/my-bucket/my-file.txt"

Upload local file to s3.

aws-curl --request PUT \
  --data "@my-file.txt" \
  --region "us-east-1" \
  "https://s3.amazonaws.com/my-bucket/my-file.txt"

Upload buffer to s3.

aws-curl --request PUT \
  --data "my content" \
  --region "us-east-1" \
  "https://s3.amazonaws.com/my-bucket/my-file.txt"

Delete file from s3:

aws-curl --request DELETE \
  --region "us-east-1" \
  "https://s3.amazonaws.com/sormy/test.txt"

Example 4: EC2

Create AMI image:

aws-curl --request POST \
  --header "Content-Type: application/x-www-form-urlencoded" \
  --data "Action=CreateImage" \
  --data "Version=2016-11-15" \
  --data "InstanceId=i-something" \
  --data "Name=My Image Name" \
  --data "Description=My Image Description" \
  --data "NoReboot=true" \
  --data "BlockDeviceMapping.1.DeviceName=/dev/xvdb" \
  --data "BlockDeviceMapping.1.NoDevice=1" \
  --data "DryRun=true" \
  --region "us-east-1" \
  "https://ec2.amazonaws.com"

Terminate EC2 instance:

aws-curl --request POST \
  --header "Content-Type: application/x-www-form-urlencoded" \
  --data "Action=TerminateInstances" \
  --data "Version=2016-11-15" \
  --data "InstanceId.1=i-something" \
  --data "DryRun=true" \
  --region "us-east-1" \
  "https://ec2.amazonaws.com"

Command line arguments

aws-curl is very thin wrapper around curl. Most of options are passed as it is to curl with some exceptions (see below).

Wrapper recognizes these curl arguments:

  • --url as explicit request URL (but can be provided only once)
  • https://*.amazonaws.com somewhere in argument list as request URL
  • Last argument as url if not explicitly provided using --url and if there is no argument that looks like AWS service endpoint https://*.amazonaws.com
  • -X | --request as request METHOD (GET is default)
  • -H | --header as request header
  • -d | --data as request body (but passed to curl as --data-binary)
  • -V | --version - shows version of aws-curl and curl
  • -h | --help - shows help for aws-curl and curl
  • -v | --verbose - dumps debug details (in addition to curl debug details)

Wrapper recognizes these non-curl arguments:

  • --service - AWS service name, if can't be automatically detected from host
  • --region - AWS region name, if can't be automatically detected from host or if not explicitly provided in AWS_DEFAULT_REGION environment variable
  • --ec2-creds - use attached to EC2 credentials (instance role)

Response format

APIs for different services have different default response format. Sometimes it is json, sometimes xml. For most APIs you could enforce json output format by adding header Accept: application/json and xml output format by adding header Accept: application/xml.

Automatically computed headers

These headers are automatically handled by aws-curl:

  • Host - curl computes it automatically based on URL
  • x-amz-date - generated based on current date/time
  • x-amz-content-sha256 - added automatically if request is to s3 service
  • x-amz-security-token - added automatically if corresponding env variable is set
  • Authorization - automaticaly generated based on request and AWS credentials
  • Content-Length - curl computes it automatically
  • Connection - curl inserts it if needed

Some headers provided by default by curl are unset by aws-curl:

  • User-Agent - doesn't have any impact on response
  • Accept - optional, but can be used to enforce response format (xml or json)
  • Content-Type - can be required or not depending on API

Service/region autodetection

Wrapper tries to auto detect AWS region name and AWS service name from service endpoint host.

Assumed format for endpoint is https://<service>.<region>.<domain> or https://<service>.<domain>, for example https://logs.us-east-1.amazonaws.com and https://sts.amazonaws.com.

Read more about AWS service endpoints: https://docs.aws.amazon.com/general/latest/gr/rande.html

Wrapper implicitly adds headers authorization, x-amz-date, x-amz-content-sha256 and x-amz-security-token (if needed), so don't need to pass them explicitly.

How to get know syntax for API

AWS documentation

Take a look on AWS documentation, in most cases it has explicit http request example.

The documentation is available here: https://docs.aws.amazon.com

AWS CLI

Download and install AWS CLI: https://aws.amazon.com/cli/

Run the same command using aws cli with --debug. Take a look how AWS CLI is performing the request, what body is used, what method is used, what url, what region and what headers. Take a look on Content-Type, it impacts on how request body should be encoded.

You can get more details by exploring service json metadata file. AWS CLI with --debug dumps what service file is loaded for specific command. You can explore it and find what body format is, what are all available options and what is the result.

EC2 attached role

This repo includes ec2-import-creds that can import attached credentials including access key, secret key, session token and region.

Just import from the shell as source ec2-import-creds.

Or you can use --ec2-creds options of aws-cli to get the same effect, but importing credentials once in beginning is faster than importing for every aws-curl invocation.

Platforms

The script has been tested on bash in posix mode on macOS and Linux. It should work on other shells and OS as well. If not, please cut a ticket.

License

MIT