[Tailscale] is really good. I’ve been using it as a virtual private network to span 2 home networks and to securely (!) access my hosts when I’m remote.

Recently Tailscale added Webhook functionality to permit processing subscribed-to (Tailscale) events. I’m always a sucker for a webhook ;-)

Here’s a curl command to send a test event to a Tailscale Webhook:

URL=""

# From Tailscale's docs
# https://tailscale.com/kb/1213/webhooks/#events-payload
BODY='
[
  {
    "timestamp": "2022-09-21T13:37:51.658918-04:00",
    "version": 1,
    "type": "test",
    "tailnet": "example.com",
    "message": "This is a test event",
    "data": null
  }
]
'

T=$(date +%s)
V=$(\
  printf "${T}.${BODY}" \
  | openssl dgst -sha256 -hmac "${SECRET}" -hex -r \
  | head --bytes=64)

curl \
--request POST \
--header "Tailscale-Webhook-Signature:t=${T},v1=${V}" \
--header "Content-Type: application/json" \
--data "${BODY}" \
https://${URL}

There must be a better way of extracting the hashed value from the openssl output.

Table of Contents

• Artifacts
• Pushover
• Caveat
• Cloud Monitoring Webhook
• Cloud Functions
• Cloud Run

Artifacts

• GitHub: go-gcp-pushover-notificationchannel
• Image: ghcr.io/dazwilkin/go-gcp-pushover-notificationchannel:220515

Pushover

Logging in to your Pushover account, you will be presented with a summary|dashboard page that includes Your User Key. Copy the value of this key into a variable called PUSHOVER_USER

Create New Application|API Token

Pushover API has a Pushing Messages method. The documentation describes the format of the HTTP Request. It must be a POST using TLS (https://) to https://api.pushover.net/1/messages.json. The content-type should be application/json. In the JSON body of the message, we must include token (PUSHOVER_TOKEN), user (PUSHOVER_USER_KEY), device (we’ll use cloud-monitoring) and a title and a message

I developed an admission webhook for Akri, twice (Golang, Rust). I naively followed other examples for the generation of the certificates, created a 1.20 cluster and broke that process.

I’d briefly considered using cert-manager recently but quickly abandoned the idea thinking it would be onerous and unnecessary complexity for little-old-me. I was wrong. It’s excellent and I recommend it highly.

I won’t reproduce the v1beta1 and v1 examples from the Stackoverflow question as they should be self-explanatory. I suspect (!?) that I should not have used Kubernete’s (API Server’s) CA for the Webhook but it could well be that I just don’t understand the correct approach.

I spent some time last week writing my first admission webhook for Kubernetes. I wrote the handler in Golang because I’m most familiar with Golang and because, as Kubernetes’ native language, I was more confident that the necessary SDKs would exist and that the documentation would likely use Golang by default. I struggled to find useful documentation and so this post is to help you (and me!) remember how to do this next time!