75 lines
2.5 KiB
Go
75 lines
2.5 KiB
Go
package awsutil
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import (
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"net/http"
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"time"
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"github.com/aws/aws-sdk-go/aws"
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"github.com/aws/aws-sdk-go/aws/ec2metadata"
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"github.com/aws/aws-sdk-go/aws/session"
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"github.com/hashicorp/errwrap"
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)
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// "us-east-1 is used because it's where AWS first provides support for new features,
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// is a widely used region, and is the most common one for some services like STS.
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const DefaultRegion = "us-east-1"
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// This is nil by default, but is exposed in case it needs to be changed for tests.
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var ec2Endpoint *string
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/*
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It's impossible to mimic "normal" AWS behavior here because it's not consistent
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or well-defined. For example, boto3, the Python SDK (which the aws cli uses),
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loads `~/.aws/config` by default and only reads the `AWS_DEFAULT_REGION` environment
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variable (and not `AWS_REGION`, while the golang SDK does _mostly_ the opposite -- it
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reads the region **only** from `AWS_REGION` and not at all `~/.aws/config`, **unless**
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the `AWS_SDK_LOAD_CONFIG` environment variable is set. So, we must define our own
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approach to walking AWS config and deciding what to use.
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Our chosen approach is:
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"More specific takes precedence over less specific."
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1. User-provided configuration is the most explicit.
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2. Environment variables are potentially shared across many invocations and so they have less precedence.
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3. Configuration in `~/.aws/config` is shared across all invocations of a given user and so this has even less precedence.
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4. Configuration retrieved from the EC2 instance metadata service is shared by all invocations on a given machine, and so it has the lowest precedence.
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This approach should be used in future updates to this logic.
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*/
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func GetRegion(configuredRegion string) (string, error) {
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if configuredRegion != "" {
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return configuredRegion, nil
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}
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sess, err := session.NewSessionWithOptions(session.Options{
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SharedConfigState: session.SharedConfigEnable,
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})
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if err != nil {
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return "", errwrap.Wrapf("got error when starting session: {{err}}", err)
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}
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region := aws.StringValue(sess.Config.Region)
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if region != "" {
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return region, nil
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}
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metadata := ec2metadata.New(sess, &aws.Config{
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Endpoint: ec2Endpoint,
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EC2MetadataDisableTimeoutOverride: aws.Bool(true),
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HTTPClient: &http.Client{
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Timeout: time.Second,
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},
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})
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if !metadata.Available() {
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return DefaultRegion, nil
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}
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region, err = metadata.Region()
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if err != nil {
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return "", errwrap.Wrapf("unable to retrieve region from instance metadata: {{err}}", err)
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}
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return region, nil
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}
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