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3 posts with the tag “aws”

How to verify that VPC traffic to S3 is going through your S3 gateway?

Gateway endpoints for Amazon S3 are a must-have whenever your EC2 instances send and receive traffic from S3, because they allow the traffic to stay within the AWS network, hence better security, bandwidth, throughput, and costs. They can easily be created, and added to your VPC route tables.

But how do you verify that traffic is indeed going through the S3 gateway, and not crossing the outer internet?

Using traceroute, you can probe the routes and see whether you are directly hitting the S3 servers (i.e. no intermediate gateway). In this example, the instance is running from a VPC located in us-east-1:

Terminal window
$ traceroute -n -T -p 443
traceroute to (, 30 hops max, 60 byte packets
1 * * *
2 * * *
3 * * *
4 * * *
5 * * *
6 0.890 ms 0.916 ms 0.892 ms
Terminal window
$ traceroute -n -T -p 443
traceroute to (, 30 hops max, 60 byte packets
1 * * *
2 * * *
3 * * *
4 * * *
5 * * *
6 0.268 ms 0.275 ms 0.252 ms

Both outputs produce the expected result, i.e. no intermediary gateway. This is what would happen if you were accessing a bucket located in the us-east-1 region.

Let’s see what happens if we try to access an S3 endpoint located in another zone:

Terminal window
$ traceroute -n -T -p 443
traceroute to (, 30 hops max, 60 byte packets
1 * * *
2 0.275 ms 0.265 ms 0.215 ms
3 0.205 ms 0.231 ms 0.206 ms
4 1.369 ms 0.648 ms 0.233 ms
5 0.326 ms * *
6 0.371 ms 0.362 ms *
7 * 0.251 ms *
8 * * *
9 * * 0.392 ms
10 * * *
11 * 1.321 ms *
12 * * 1.491 ms
13 * * 1.286 ms
14 67.909 ms 67.356 ms 67.929 ms

As you can see, the route is completely different, and as expected does not hit straight to the S3 endpoint.

TL;DR: make sure your route tables are correct, and only point to S3 buckets located in the same region.

GitHub Action runner images (AMI) for AWS EC2

As part of the RunsOn service, we automatically maintain and publish replicas of the official GitHub runner images as AWS-formatted images (AMIs).

New images are automatically released within 48h of the official upstream release, and are slightly trimmed to remove outdated software, or (mostly useless) caches.

This means the disk usage is below 30GB, making it sufficiently small to boot in around 40s. The runner binary is also preinstalled in the images.

Supported regions:

  • us-east-1
  • eu-west-1

AMIs can be found using the following search:

  • name: runs-on-ubuntu22-full-x64-*
  • owner 135269210855

You can find more details on

Automatically cleanup outdated AMIs in all AWS regions

Here is a script you can use to automatically cleanup AMIs older than 60 days (configurable), while keeping the 2 most recent AMIs in each region. This helps to remove outdated images, as well as reducing storage costs for your AMIs.

Particularly useful in the case of, where we regularly rebuild base images whenever GitHub releases a new version of the image runner.

The bin/cleanup script (simply adjust the filters as needed):

# Deregisters old AMIs and deletes associated snapshots, in all regions
set -e
set -o pipefail
REGIONS="$(aws ec2 describe-regions --query "Regions[].RegionName" --output text)"
# Number of days to keep AMIs
# Define the age threshold in seconds (60 days)
# Get the current timestamp in seconds since epoch
for region in ${REGIONS[@]}; do
echo "---- Region: ${region} ---"
# List all your AMIs and extract relevant information using the AWS CLI
image_count=$(aws ec2 describe-images --owner self --filters "Name=tag:application, Values=${APPLICATION}" --query 'length(Images)' --region "$region" --output text)
echo " Total AMIs in this region: ${image_count}"
if [ "$image_count" -lt 2 ]; then
echo " Less than 2 AMIs found, skipping"
aws ec2 describe-images --owner self --region "${region}" --filters "Name=tag:application, Values=${APPLICATION}" --query 'Images[*].[Name,ImageId,CreationDate]' --output text | \
while read -r name image_id creation_date; do
# Parse the creation date into seconds since epoch
image_timestamp=$(date -d "$creation_date" +%s)
# Calculate the age of the AMI in seconds
age=$((CURRENT_TIMESTAMP - image_timestamp))
# Check if the AMI is older than the threshold
if [ $age -gt $AGE_THRESHOLD ]; then
echo " ! Deregistering AMI: ${image_id} (${name}) created on $creation_date"
snapshot_id=$(aws ec2 describe-images --image-ids "$image_id" --query "Images[].BlockDeviceMappings[].Ebs.SnapshotId" --region "${region}" --output text)
if [ "$DRY_RUN" = "true" ]; then
echo " DRY_RUN is set to true, skipping deregistering AMI ${image_id} and deleting snapshot ${snapshot_id}"
aws ec2 deregister-image --image-id "$image_id" --region "${region}"
echo " ! Deleting snapshot ${snapshot_id} for AMI ${image_id}"
aws ec2 delete-snapshot --snapshot-id "${snapshot_id}" --region "${region}"

Example output:

---- Region: ap-southeast-2 ---
Total AMIs in this region: 0
---- Region: eu-central-1 ---
Total AMIs in this region: 5
Deregistering AMI: ami-0576e83d0a0f89fbe (runner-ubuntu2204-1699888130) created on 2023-11-13T16:53:48.000Z
Deleting snapshot snap-07db95a7f230d3f76 for AMI ami-0576e83d0a0f89fbe
Deregistering AMI: ami-004d4d18e6db2f812 (runner-ubuntu-22-1699873337) created on 2023-11-13T12:40:48.000Z
Deleting snapshot snap-0500b0e3fb95ab36a for AMI ami-004d4d18e6db2f812
Deregistering AMI: ami-0e6239eae649effcd (runner-ubuntu22-20231115.7-1700233930) created on 2023-11-17T17:01:58.000Z
Deleting snapshot snap-05e795e4c6fe9e66f for AMI ami-0e6239eae649effcd
Deregistering AMI: ami-0dd7f6b263a3ce28c (runner-ubuntu22-20231115-1700156105) created on 2023-11-16T19:24:38.000Z
Deleting snapshot snap-02c1aef800c429b76 for AMI ami-0dd7f6b263a3ce28c
---- Region: us-east-1 ---
Total AMIs in this region: 4
Deregistering AMI: ami-0b56f2d6af0d58ce0 (runner-ubuntu2204-1699888130) created on 2023-11-13T15:54:22.000Z
Deleting snapshot snap-0f2e8759bea8f3937 for AMI ami-0b56f2d6af0d58ce0
Deregistering AMI: ami-04266841492472a95 (runner-ubuntu22-20231115.7-1700233930) created on 2023-11-17T16:02:34.000Z
Deleting snapshot snap-0f0fcf9c6406c3ad9 for AMI ami-04266841492472a95
Deregistering AMI: ami-0738c7108915044fe (runner-ubuntu22-20231115-1700156105) created on 2023-11-16T18:21:40.000Z
Deleting snapshot snap-03f16588f59ed7cea for AMI ami-0738c7108915044fe

Example GitHub Action workflow file to schedule a cleanup every night:

name: Cleanup
group: ${{ github.workflow }}-${{ github.ref }}
- cron: '0 2 * * *'
timeout-minutes: 30
runs-on: ubuntu-latest
- uses: actions/checkout@v4
- name: Configure AWS credentials
uses: aws-actions/configure-aws-credentials@v4
aws-access-key-id: ${{ secrets.AWS_ACCESS_KEY_ID }}
aws-secret-access-key: ${{ secrets.AWS_SECRET_ACCESS_KEY }}
aws-region: us-east-1
- run: bin/cleanup