The Tool Desk
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Use this Compose configuration
Uptime Kuma’s documented Compose deployment uses the louislam/uptime-kuma:2 image, stores application data at /app/data, and listens on container port 3001. Add the healthcheck alongside the existing port, volume and restart settings:
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services:
uptime-kuma:
image: louislam/uptime-kuma:2
ports:
- "3001:3001"
volumes:
- uptime-kuma-data:/app/data
restart: unless-stopped
healthcheck:
test: ["CMD", "curl", "-f", "http://localhost:3001"]
interval: 30s
timeout: 10s
retries: 5
start_period: 30s
volumes:
uptime-kuma-data:Save the change in your Compose file, then recreate or update the service with docker compose up -d. The values above are a reasonable policy for many installations, not a performance benchmark. If your host takes longer to start Kuma, increase start_period rather than declaring the container unhealthy during normal startup.
Why the probe uses localhost:3001
Compose executes a service healthcheck inside that service’s container. Inside the Uptime Kuma container, the application’s listener is on port 3001, so the probe should call http://localhost:3001. It does not need to use the host-published address.
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The mapping 3001:3001 has two sides: the first port is on the Docker host and the second is inside the container. A browser or monitoring system outside Docker uses the host side. The healthcheck is already inside the container and can reach the second side directly through its loopback interface.
Using the host address in an in-container check adds unnecessary routing and can fail because of firewall rules, hairpin NAT, DNS differences or a host address that is not reachable from the container. It also tests a different path from the one Kuma itself uses. Probe the process where it actually listens unless you deliberately want to test an external route.
What the test command does
Docker defines healthcheck.test as the command used to determine whether a container is healthy. In list form, the first element selects the execution mode. CMD runs the following arguments directly, while CMD-SHELL runs a shell command. NONE disables a healthcheck inherited from an image.
The recommended entry is:
test: ["CMD", "curl", "-f", "http://localhost:3001"]curl makes an HTTP request. The -f (fail) option causes curl to return a failure status for an HTTP error response, allowing Docker to count that probe as failed. Without -f, curl can return success after receiving an HTTP error page, which would make the health signal less useful.
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Check that the exact Uptime Kuma image tag you deploy contains curl before relying on this command. A healthcheck cannot run a binary that is absent from the image. If your chosen image variant does not include curl, select another HTTP client that is actually installed and express its command in the same test field. Do not copy a command merely because it works in a different image.
Healthcheck settings and how to tune them
Each timing field changes how quickly Docker changes the reported state:
| Setting | Meaning | Starting value | What changing it does |
|---|---|---|---|
interval |
Time between completed probes during normal operation. | 30s | A shorter interval detects failures sooner but generates more requests and log activity. |
timeout |
Maximum time allowed for one probe. | 10s | A shorter timeout is more sensitive to latency; a longer one tolerates slow disks, CPU pressure or congested hosts. |
retries |
Consecutive failures required before Docker marks the container unhealthy. | 5 | More retries reduce false alarms from transient failures but delay the unhealthy state. |
start_period |
Startup grace period during which failures do not count toward the retry limit. | 30s | Increase it when Kuma’s observed startup time is longer than 30 seconds. |
start_interval |
Optional startup probe interval in Compose versions that support it. | Not set | Use it when you need a different probe cadence during startup; confirm your installed Compose version supports the field. |
These controls are independent. For example, five failures at a 30-second interval can take roughly two and a half minutes to reach an unhealthy state, depending on probe timing and startup rules. That delay is intentional tolerance, not a promise that every failure will be detected on an exact schedule.
Apply the change and inspect the result
- Edit the Compose file and add the healthcheck under the
uptime-kumaservice. Keep the indentation underhealthcheckcorrect; YAML indentation determines which service owns the setting. - Apply the configuration with
docker compose up -d. Compose will create the container or replace it when the service definition requires recreation. - Check the summarized state with
docker compose ps. The service should eventually show a healthy status after successful probes. - For the complete health record, first obtain the container ID and then inspect its health state:
docker compose ps -q uptime-kuma
docker inspect $(docker compose ps -q uptime-kuma) --format '{{json .State.Health}}'The detailed output includes the current status, failing streak and recent probe results. Run these commands yourself on the host; the configuration is not considered verified merely because Compose accepted the YAML.
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Health status is not an automatic restart mechanism
A healthcheck reports state. It does not restart a process simply because Docker labels the container unhealthy. Keep a separate restart policy when you want Docker to start the container again after its main process exits. The example uses restart: unless-stopped, which is a restart-policy choice and should be evaluated separately from probe timing.
An unhealthy status can therefore coexist with a running container. Kuma’s process may still exist while its HTTP listener is unavailable, it is blocked on storage, or it is returning HTTP errors. Conversely, a process that exits may be restarted by the restart policy before a healthcheck can provide useful information. Treat the two signals as different diagnostic channels:
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- Health state: whether the configured command can complete successfully within its timeout and retry policy.
Make another Compose service wait for Kuma
If a dependent service must not be created until Uptime Kuma is responding, Docker Compose supports a health-based dependency condition. Put the condition on the dependent service’s depends_on entry:
services:
uptime-kuma:
image: louislam/uptime-kuma:2
ports:
- "3001:3001"
volumes:
- uptime-kuma-data:/app/data
restart: unless-stopped
healthcheck:
test: ["CMD", "curl", "-f", "http://localhost:3001"]
interval: 30s
timeout: 10s
retries: 5
start_period: 30s
dependent-service:
image: example/dependent-service
depends_on:
uptime-kuma:
condition: service_healthy
volumes:
uptime-kuma-data:With condition: service_healthy, Compose waits for the dependency’s healthcheck to pass before creating the dependent service. This coordinates startup; it does not continuously restart the dependent service if Kuma later becomes unhealthy. The dependent service still needs its own failure handling.
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Choosing between common probe patterns
| Pattern | Use when | Trade-off |
|---|---|---|
curl -f http://localhost:3001 |
You want HTTP errors to count as probe failures and curl is installed. | Requires curl in the image; strict about HTTP error responses. |
curl -L localhost:3001 |
You are following a published example that allows redirects and your image has curl. | Without -f, an HTTP error response may not produce a failing exit status. |
| A different installed HTTP client | Your image does not contain curl but includes another suitable client. | The exact flags and failure behavior depend on that client; verify them inside the image. |
| An external host route | You intentionally need to test reachability through a proxy, published port or external DNS path. | It tests networking outside Kuma’s own listener and can fail for reasons unrelated to the application. |
The two published Uptime Kuma Compose examples use the same in-container port but different policies: one uses curl -L localhost:3001 with a 30-second interval, 10-second timeout, five retries and a two-minute startup period; another uses curl -f http://localhost:3001 with a 30-second interval, three retries, a 10-second startup period and a five-second timeout. These are tolerance choices, not universal constants. Pick values based on observed startup and the cost of delayed failure detection.
Troubleshoot an unhealthy Kuma container
The probe reports “executable file not found”
The image does not contain the command named in test, or the command is not on the image’s executable path. Confirm the tools available in the exact image tag you run, then change the probe to an installed client. Do not solve this by probing the host, because that would hide the missing in-container dependency.
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Compare the host’s observed startup time with start_period. Increase the grace period when startup is legitimately slow, and use docker compose ps plus the detailed health output to distinguish startup delay from a persistent failure. Increasing timeout helps only when the application eventually responds slowly; it does not fix a listener that never starts.
The container stays unhealthy after startup
Check the health log from docker inspect, then test the same endpoint from inside the container with the same client and URL. A failed HTTP request can indicate that Kuma is not listening on port 3001, the process is still initializing, or the application is returning an error. Keep the target as localhost:3001 unless you have intentionally changed Kuma’s listening configuration.
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The container restarts but health never becomes healthy
Inspect both the restart count and health output. A restart policy may be reacting to process exits while the healthcheck is reporting a separate HTTP problem. Review container logs and storage errors rather than assuming that changing retries will repair the underlying failure.
Keep storage reliability separate from HTTP health
Uptime Kuma stores its application data under /app/data. The project warns that NFS (Network File System) filesystems are not supported for this data directory and recommends mapping it to a local directory or Docker volume. The named volume in the example keeps that data separate from the container lifecycle.
A passing HTTP probe does not prove that every database operation is safe, and a failing probe cannot repair a filesystem problem. When diagnosing incidents, check the health output, container logs and the reliability of the volume independently. If the data directory is on unsupported NFS storage, move it to supported local storage before tuning probe thresholds.
Quick Recap
Practical checklist
- Use the documented image tag
louislam/uptime-kuma:2or confirm the healthcheck command for the image you actually selected. - Persist
/app/dataon a local directory or Docker volume, not NFS. - Probe
http://localhost:3001from inside the container. - Use
curl -fwhen curl is present and you want HTTP errors to fail the check. - Set
interval,timeout,retriesandstart_periodaccording to observed startup and acceptable detection delay. - Keep a separate
restartpolicy if you need automatic recovery after process exit. - Run
docker compose up -d, then verify withdocker compose psanddocker inspect. - Use
condition: service_healthyonly when a dependent Compose service must wait for Kuma during creation.
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