rustfs/docs/operations/rolling-restart.md

Restarting a multi-node RustFS cluster

How to restart nodes of an erasure-coded multi-node cluster without losing availability, what to expect when several nodes are down at once (sequential cold start), and how to read the degraded-mode signals. Written for the failure pattern reported in rustfs/rustfs#4304.

Upgrading the binary or container image never changes the on-disk data format. Replacing the executable and restarting is safe; no migration step runs on startup.

Warning

The release that switches local SSE wrapped DEKs from the legacy base64(nonce):base64(ciphertext) representation to the versioned JSON envelope is a deliberate exception. Do not run that release together with an older RustFS version: older nodes cannot read objects written with the JSON envelope. Freeze every source of object mutation, including client writes and background lifecycle or replication work, upgrade every node, and then resume traffic. Downgrading or rolling back after new encrypted objects are written is not supported.

TL;DR

• Rolling restart (no downtime): restart one node at a time, and wait for the restarted node to report 200 on /health/ready before touching the next one. The remaining nodes keep serving traffic.
• Sequential cold start (several nodes down): nodes started before the cluster has quorum come up in degraded mode — the process stays alive, answers 503 with the blocking reason, and recovers automatically as soon as enough peers are online. Do not restart-loop them; just keep starting the remaining nodes.

Why a single node cannot serve alone

Erasure coding shards every object (including internal metadata such as IAM users, groups, and policies under .rustfs.sys) across the drives of a set. Reading an object back needs a read quorum of shards online. With the drives of one set spread over several nodes, one node alone can never satisfy the read quorum — this is a mathematical property of erasure coding, not a bug. The cluster becomes readable once enough nodes are up (for internal configuration objects, which are written with maximum parity, that is typically about half the nodes of a set).

Distributed locking similarly needs a majority of nodes' lock RPC endpoints. The startup path no longer takes namespace locks while loading IAM (rustfs/rustfs#4363), so IAM recovery depends only on the storage read quorum.

Rolling restart procedure

For each node, in any order, one at a time:

1. Restart the node (upgrade the binary/image first if this is an upgrade).

2. Wait until the node reports ready:

   curl -fsS http://<node>:9000/health/ready
   

   A ready node returns 200 with "ready": true in the JSON body.

3. Only then move on to the next node.

While one node is down, the rest of the cluster keeps quorum and serves all traffic. If you take a second node down before the first is back, some erasure sets may lose write or even read quorum and requests start failing — this is the situation to avoid.

Sequential cold start (multiple nodes down)

When the whole cluster (or several nodes) went down — power loss, host maintenance, crash-looping deployment — and nodes are brought back one at a time:

1. Early nodes come up degraded. The process does not exit. S3 requests receive 503 Service Unavailable with a Retry-After: 5 header, an x-rustfs-readiness-pending header, and a body naming the blocking dependency:

   • storage_quorum — waiting for enough nodes/disks for the erasure read quorum;
   • iam — storage is up, IAM cache is still loading;
   • startup_finalization — last startup steps are being published.

2. Logs say what the node waits for. The IAM recovery loop retries with backoff and logs event="iam_bootstrap_retry_failed" with an actionable hint field (for example, "storage read quorum not met yet; waiting for enough cluster nodes/disks to come online"). After repeated failures the log level escalates from WARN to ERROR — this still does not kill the process.

3. Recovery is automatic. As soon as enough peers are online for the storage read quorum, the pending nodes finish IAM bootstrap on the next retry and flip /health/ready to 200 on their own. No manual restart is needed, and restarting them does not speed anything up.

4. Check readiness detail while waiting. /health/ready (and /minio/health/ready) return per-dependency detail during degradation:

   curl -s http://<node>:9000/health/ready | jq
   

   The details object shows storage / iam / lock readiness, and degradedReasons lists machine-readable causes such as storage_quorum_unavailable or lock_quorum_unavailable.

Tuning

• RUSTFS_STARTUP_READINESS_MAX_WAIT_SECS (default 120): how long startup waits for full readiness before continuing in degraded mode with background recovery. Raising it delays the listener during genuinely slow starts; lowering it surfaces degraded mode sooner. Recovery retries continue regardless of this limit.

What is not normal

• A node process exiting with a fatal IAM/lock error during startup — that fatal path was removed after v1.0.0-beta.5 (rustfs/rustfs#4304); upgrade if you still see it.
• A node stuck degraded after the whole cluster is back: check network reachability between nodes (peer RPC ports) and per-node clocks, then inspect degradedReasons and the hint field of the IAM retry logs.
• A node shown offline in the console with no log output — tracked separately, see rustfs/backlog#888.