# Silo Healthcheck

Silo server exposes three un-authenticated, healthcheck endpoints liveness probe and a cluster probe at `/minio/health/live` and `/minio/health/cluster` respectively.

## Native CLI probe

The `silo` binary can probe those endpoints itself, which makes health checking possible in containers that ship no shell, `curl`, or `mc`:

```
silo healthcheck [FLAGS] [live|ready|cluster|cluster-read]
```

The check name maps 1:1 onto `/minio/health/<path>`; `live` is the default. The exit code is `0` when healthy and `1` otherwise, and one diagnostic line (including the `x-minio-server-status` and quorum headers on failure) is printed for `docker inspect` to capture. The probe target is derived the same way the server derives its own listen address — `--address` / `MINIO_ADDRESS`, with HTTPS auto-detected from `public.crt` and `private.key` in `--certs-dir` — or overridden wholesale with `--url` / `MINIO_HEALTHCHECK_URL`. The environment form exists for containers with a baked-in `HEALTHCHECK`: a probe process cannot see the server's command line, so when the server's address or TLS setup comes from CLI arguments rather than the environment, set `MINIO_HEALTHCHECK_URL` (e.g. `https://127.0.0.1:9010`) to point the built-in probe at it. Certificate verification is skipped, matching the kubelet's behavior for HTTPS probes.

Use it as an image `HEALTHCHECK` (exec form, since there may be no shell; keep the outer timeout above the probe's own 5s deadline so its diagnostic line survives):

```
HEALTHCHECK --interval=30s --timeout=10s --start-period=2m --start-interval=2s --retries=3 \
  CMD ["/usr/bin/silo", "healthcheck", "ready"]
```

or as a Docker Compose healthcheck:

```
healthcheck:
  test: ["CMD", "/usr/bin/silo", "healthcheck", "ready"]
  interval: 5s
  timeout: 10s
  retries: 5
```

`silo healthcheck --maintenance cluster` answers the pre-drain question documented below: exit `0` when the node can be taken down safely, exit `1` (HTTP 412) when doing so would lose HA. Keep the `cluster` checks out of per-container liveness probes — they reflect cluster-wide quorum, not this process.

## Liveness probe

This probe always responds with '200 OK'. Only fails if 'etcd' is configured and unreachable. When liveness probe fails, Kubernetes like platforms restart the container.

```
livenessProbe:
  httpGet:
    path: /minio/health/live
    port: 9000
    scheme: HTTP
  initialDelaySeconds: 120
  periodSeconds: 30
  timeoutSeconds: 10
  successThreshold: 1
  failureThreshold: 3
```

## Readiness probe

This probe always responds with '200 OK'. Only fails if 'etcd' is configured and unreachable. When readiness probe fails, Kubernetes like platforms turn-off routing to the container.

```
readinessProbe:
  httpGet:
    path: /minio/health/ready
    port: 9000
    scheme: HTTP
  initialDelaySeconds: 120
  periodSeconds: 15
  timeoutSeconds: 10
  successThreshold: 1
  failureThreshold: 3
```

## Cluster probe

### Cluster-writeable probe

The reply is '200 OK' if cluster has write quorum if not it returns '503 Service Unavailable'.

```
curl http://silo1:9001/minio/health/cluster
HTTP/1.1 503 Service Unavailable
Accept-Ranges: bytes
Content-Length: 0
Server: Silo
Vary: Origin
X-Amz-Bucket-Region: us-east-1
X-Minio-Write-Quorum: 3
X-Amz-Request-Id: 16239D6AB80EBECF
X-Xss-Protection: 1; mode=block
Date: Tue, 21 Jul 2020 00:36:14 GMT
```

### Cluster-readable probe

The reply is '200 OK' if cluster has read quorum if not it returns '503 Service Unavailable'.

```
curl http://silo1:9001/minio/health/cluster/read
HTTP/1.1 503 Service Unavailable
Accept-Ranges: bytes
Content-Length: 0
Server: Silo
Vary: Origin
X-Amz-Bucket-Region: us-east-1
X-Minio-Write-Quorum: 3
X-Amz-Request-Id: 16239D6AB80EBECF
X-Xss-Protection: 1; mode=block
Date: Tue, 21 Jul 2020 00:36:14 GMT
```

### Checking cluster health for maintenance

You may query the cluster probe endpoint to check if the node which received the request can be taken down for maintenance, if the server replies back '412 Precondition Failed' this means you will lose HA. '200 OK' means you are okay to proceed.

```
curl http://silo1:9001/minio/health/cluster?maintenance=true
HTTP/1.1 412 Precondition Failed
Accept-Ranges: bytes
Content-Length: 0
Server: Silo
Vary: Origin
X-Amz-Bucket-Region: us-east-1
X-Amz-Request-Id: 16239D63820C6E76
X-Xss-Protection: 1; mode=block
X-Minio-Write-Quorum: 3
Date: Tue, 21 Jul 2020 00:35:43 GMT
```