We’ve all been there. You perform a routine maintenance run—sudo apt update && sudo apt upgrade—followed by a quick reboot to keep the kernel fresh. Your services start coming back online, but when you log into Portainer to check your containers, you’re greeted with a sight that makes every sysadmin’s heart sink: the “Local” environment is marked as “Down.”
If you recently updated your Linux server (specifically in late 2025), you likely didn’t break anything. You simply ran into a major version shift in the Docker ecosystem.
The Symptom: The “Red Dot” of Doom
After the update, Portainer might show a red “Down” status for your local endpoint. Clicking into it usually yields a vague error like:
“Failure: Ready state check failed: Environment is unreachable.”
Or, if you dig into the logs, you might see a more cryptic message regarding API version mismatches. Everything else on your server is running fine, but Portainer has suddenly lost the ability to “talk” to the very engine it is running on.
The “Why”: Docker 29 and the API Floor
The culprit is Docker Engine 29.x.
Historically, Docker has maintained backward compatibility for its API for a long time. However, with version 29, the Docker team increased the minimum supported API version to 1.44.
If you were running an older version of Portainer (like 2.19 or 2.21), it was trying to communicate with Docker using an older API “language” (version 1.24 or 1.25). Docker 29 simply stopped listening to that older language. It’s like trying to order coffee in a language the barista no longer speaks—the connection is there, but the communication is broken.
The Solution: The Two-Step Recovery
1. Upgrade Portainer
The most effective fix is to bring Portainer up to date. The Portainer team released versions 2.33.5 LTS and 2.36.0 STS specifically to handle the new requirements of Docker 29.
To fix it, you need to pull the latest image and recreate the container:
Bash
# Stop and remove the old version (your data is safe in its volume)
docker stop portainer
docker rm portainer
# Pull the latest image
docker pull portainer/portainer-ce:latest
# Re-run your deployment command
docker run -d -p 9443:9443 -p 8000:8000 --name portainer --restart=always \
-v /var/run/docker.sock:/var/run/docker.sock \
-v portainer_data:/data \
portainer/portainer-ce:latest
Once updated, Portainer will automatically use the correct API version, and your “Local” environment should snap back to “Green/Up” status.
2. Don’t Forget Your Watchtower
If you use Watchtower to automate your updates, it might be suffering from the same “blindness.” Since Watchtower also talks to the Docker API to check for image updates, an outdated Watchtower container will fail to see your other services.
You can verify it’s working by running a manual check:
Bash
docker run --rm -v /var/run/docker.sock:/var/run/docker.sock containrrr/watchtower --run-once
If it reports Found new image or No new images found, you’re in the clear. If it throws an API error, you simply need to recreate your Watchtower container using the latest image.
Pro-Tip: Keeping it Tidy
While updates are great, they often leave behind “ghost” images (the old versions of the containers you just updated). To keep your disk space from ballooning, I recommend adding the cleanup flag to your Watchtower configuration:
Set this environment variable: WATCHTOWER_CLEANUP=true
This ensures that once a new version of a service is successfully pulled and started, the old, bulky image is deleted automatically.
Summary
Updates are essential for security, but major version jumps in Docker Engine can occasionally break the bridges between your management tools. By keeping Portainer and Watchtower updated alongside your host system, you ensure your stack remains stable and visible.
Status: Resolved ✅
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