kubernetes.github.io/docs/tasks/administer-cluster: operating etcd clusters
Radhika Puthiyetath
Andrew Chen
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assignees:
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- mml
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- wojtek-t
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title: Configure, Upgrade, and Roll Back etcd
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title: Operating etcd clusters for Kubernetes
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redirect_from:
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- "/docs/concepts/storage/etcd-store-api-object/"
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- "/docs/concepts/storage/etcd-store-api-object.html"
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@ -16,9 +16,7 @@ redirect_from:
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- "/docs/concepts/cluster-administration/etcd-upgrade.html"
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---
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[etcd](https://coreos.com/etcd/docs/latest/) is a highly-available key value
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store which Kubernetes uses for persistent storage of all of its REST API
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objects.
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etcd is a strong, consistent, and highly-available key value store which Kubernetes uses for persistent storage of all of its API objects. This documentation provides specific instruction on operating, upgrading, and rolling back etcd clusters for Kubernetes. For in-depth information on etcd, see [etcd documentation](https://github.com/coreos/etcd/blob/master/Documentation/docs.md).
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<!-- TODO(mml): Write this doc.
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@ -27,36 +25,196 @@ see _some doc_.
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-->
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## Important assumptions
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## Prerequisites
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* Run etcd as a cluster of odd members.
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* etcd is a leader-based distributed system. Ensure that the leader periodically send heartbeats on time to all followers to keep the cluster stable.
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* Ensure that no resource starvation occurs.
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Performance and stability of the cluster is sensitive to network and disk IO. Any resource starvation can lead to heartbeat timeout, causing instability of the cluster. An unstable etcd indicates that no leader is elected. Under such circumstances, a cluster cannot make any changes to its current state, which implies no new pods can be scheduled.
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* Keeping stable etcd clusters is critical to the stability of Kubernetes clusters. Therefore, run etcd clusters on dedicated machines or isolated environments for [guaranteed resource requirements](https://github.com/coreos/etcd/blob/master/Documentation/op-guide/hardware.md#hardware-recommendations).
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## Resource requirements
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Operating etcd with limited resources is suitable only for testing purposes. For deploying in production, advanced hardware configuration is required. Before deploying etcd in production, see [resource requirement reference documentation](https://github.com/coreos/etcd/blob/master/Documentation/op-guide/hardware.md#example-hardware-configurations).
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## Starting Kubernetes API server
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This section covers starting a Kubernetes API server with an etcd cluster in the deployment.
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### Single-node etcd cluster
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Use a single-node etcd cluster only for testing purpose.
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1. Run the following:
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``` bash
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./etcd --client-listen-urls=http://$PRIVATE_IP:2379 --client-advertise-urls=http://$PRIVATE_IP:2379
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```
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2. Start Kubernetes API server with the flag `--etcd-servers=$PRIVATE_IP:2379`.
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Replace `PRIVATE_IP` with your etcd client IP.
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### Multi-node etcd cluster
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For durability and high availability, run etcd as a multi-node cluster in production and back it up periodically. A five-member cluster is recommended in production. For more information, see [FAQ Documentation](https://github.com/coreos/etcd/blob/master/Documentation/faq.md#what-is-failure-tolerance).
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Configure an etcd cluster either by static member information or by dynamic discovery. For more information on clustering, see [etcd Clustering Documentation](https://github.com/coreos/etcd/blob/master/Documentation/op-guide/clustering.md).
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For an example, consider a five-member etcd cluster running with the following client URLs: `http://$IP1:2379`, `http://$IP2:2379`, `http://$IP3:2379`, `http://$IP4:2379`, and `http://$IP5:2379`. To start a Kubernetes API server:
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1. Run the following:
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./etcd --client-listen-urls=http://$IP1:2379, http://$IP2:2379, http://$IP3:2379, http://$IP4:2379, http://$IP5:2379 --client-advertise-urls=http://$IP1:2379, http://$IP2:2379, http://$IP3:2379, http://$IP4:2379, http://$IP5:2379
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2. Start Kubernetes API servers with the flag `--etcd-servers=$IP1:2379, $IP2:2379, $IP3:2379, $IP4:2379, $IP5:2379`.
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Replace `IP` with your client IP addresses.
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### Multi-node etcd cluster with load balancer
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To run a load balancing etcd cluster:
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1. Set up an etcd cluster.
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2. Configure a load balancer in front of the etcd cluster.
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For example, let the address of the load balancer be `$LB`.
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3. Start Kubernetes API Servers with the flag `--etcd-servers=$LB:2379`.
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## Securing etcd clusters
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Access to etcd is equivalent to root permission in the cluster so ideally only the API server should have access to it. Considering the sensitivity of the data, it is recommended to grant permission to only those nodes that require access to etcd clusters.
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To secure etcd, either set up firewall rules or use the security features provided by etcd. etcd security features depend on x509 Public Key Infrastructure (PKI). To begin, establish secure communication channels by generating a key and certificate pair. For example, use key pairs `peer.key` and `peer.cert` for securing communication between etcd members, and `client.key` and `client.cert` for securing communication between etcd and its clients. See the [example scripts](https://github.com/coreos/etcd/tree/master/hack/tls-setup) provided by the etcd project to generate key pairs and CA files for client authentication.
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### Securing communication
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To configure etcd with secure peer communication, specify flags `--peer-key-file=peer.key` and `--peer-cert-file=peer.cert`, and use https as URL schema.
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Similarly, to configure etcd with secure client communication, specify flags `--key-file=peer.key` and `--cert-file=peer.cert`, and use https as URL schema.
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### Limiting access of etcd clusters
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After configuring secure communication, restrict the access of etcd cluster to only the Kubernetes API server. Use TLS authentication to do so.
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For example, consider key pairs `k8sclient.key` and `k8sclient.cert` that are trusted by the CA `etcd.ca`. When etcd is configured with `--client-cert-auth` along with TLS, it verifies the certificates from clients by using system CAs or the CA passed in by `--trusted-ca-file` flag. Specifying flags `--client-cert-auth=true` and `--trust-ca-file=etcd.ca` will restrict the access to clients with the certificate `k8sclient.cert`.
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Once etcd is configured correctly, only clients with valid certificates can access it. To give Kubernetes API server the access, configure it with the flags `--etcd-certfile=k8sclient.cert` and `--etcd-keyfile=k8sclient.key`.
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**Note**: etcd authentication is not currently supported by Kubernetes. For more information, see see the related issue [Support Basic Auth for Etcd v2](https://github.com/kubernetes/kubernetes/issues/23398).
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## Replacing a failed etcd member
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etcd cluster achieves high availability by tolerating minor member failures. However, to improve the overall health of the cluster, replace failed members immediately. When multiple members fail, replace them one by one. Replacing a failed member involves two steps: removing the failed member and adding a new member.
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Though etcd keeps unique member IDs internally, it is recommended to use a unique name for each member to avoid human errors. For example, consider a three-member etcd cluster. Let the URLs be, member1=http://10.0.0.1, member2=http://10.0.0.2, and member3=http://10.0.0.3. When member1 fails, replace it with member4=http://10.0.0.4.
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1. Get the member ID of the failed member1:
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`etcdctl --endpoints=http://10.0.0.2,http://10.0.0.3 member list`
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The following message is displayed:
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8211f1d0f64f3269, started, member1, http://10.0.0.1:12380, http://10.0.0.1:2379
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91bc3c398fb3c146, started, member2, http://10.0.0.1:2380, http://10.0.0.2:2379
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fd422379fda50e48, started, member3, http://10.0.0.1:2380, http://10.0.0.3:2379
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2. Remove the failed member:
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`etcdctl member remove 8211f1d0f64f3269`
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The following message is displayed:
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Removed member 8211f1d0f64f3269 from cluster
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3. Add the new member:
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`./etcdctl member add member4 --peer-urls=http://10.0.0.4:2380`
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The following message is displayed:
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Member 2be1eb8f84b7f63e added to cluster ef37ad9dc622a7c4
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4. Start the newly added member on a machine with the IP `10.0.0.4`:
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```bash
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export ETCD_NAME="member4"
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export ETCD_INITIAL_CLUSTER="member2=http://10.0.0.2:2380,member3=http://10.0.0.3:2380,member4=http://10.0.0.4:2380"
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export ETCD_INITIAL_CLUSTER_STATE=existing
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etcd [flags]
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```
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5. Do either of the following:
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1. Update its `--etcd-servers` flag to make Kubernetes aware of the configuration changes, then restart the Kubernetes API server.
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2. Update the load balancer configuration if a load balancer is used in the deployment.
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For more information on cluster reconfiguration, see [etcd Reconfiguration Documentation](https://github.com/coreos/etcd/blob/master/Documentation/op-guide/runtime-configuration.md#remove-a-member).
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## Backing up an etcd cluster
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All Kubernetes objects are stored on etcd. Periodically backing up the etcd cluster data is important to recover Kubernetes clusters under disaster scenarios, such as losing all master nodes. The snapshot file contains all the Kubernetes states and critical information. In order to keep the sensitive Kubernetes data safe, encrypt the snapshot files.
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Backing up an etcd cluster can be accomplished in two ways: etcd built-in snapshot and volume snapshot.
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### Built-in snapshot
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etcd supports built-in snapshot, so backing up an etcd cluster is easy. A snapshot may either be taken from a live member with the `etcdctl snapshot save` command or by copying the `member/snap/db` file from an etcd [data directory](https://github.com/coreos/etcd/blob/master/Documentation/op-guide/configuration.md#--data-dir) that is not currently used by an etcd process. `datadir` is located at `$DATA_DIR/member/snap/db`. Taking the snapshot will normally not affect the performance of the member.
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Below is an example for taking a snapshot of the keyspace served by `$ENDPOINT` to the file `snapshotdb`:
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```sh
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ETCDCTL_API=3 etcdctl --endpoints $ENDPOINT snapshot save snapshotdb
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# exit 0
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# verify the snapshot
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ETCDCTL_API=3 etcdctl --write-out=table snapshot status snapshotdb
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+----------+----------+------------+------------+
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| HASH | REVISION | TOTAL KEYS | TOTAL SIZE |
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+----------+----------+------------+------------+
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| fe01cf57 | 10 | 7 | 2.1 MB |
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+----------+----------+------------+------------+
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```
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### Volume snapshot
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If etcd is running on a storage volume that supports backup, such as Amazon Elastic Block Store, back up etcd data by taking a snapshot of the storage volume.
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## Scaling up etcd clusters
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Scaling up etcd clusters increases availability by trading off performance. Scaling does not increase cluster performance nor capability. A general rule is not to scale up or down etcd clusters. Do not configure any auto scaling groups for etcd clusters. It is highly recommended to always run a static five-member etcd cluster for production Kubernetes clusters at any officially supported scale.
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A reasonable scaling is to upgrade a three-member cluster to a five-member one, when more reliability is desired. See [etcd Reconfiguration Documentation](https://github.com/coreos/etcd/blob/master/Documentation/op-guide/runtime-configuration.md#remove-a-member) for information on how to add members into an existing cluster.
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## Restoring an etcd cluster
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etcd supports restoring from snapshots that are taken from an etcd process of the [major.minor](http://semver.org/) version. Restoring a version from a different patch version of etcd also is supported. A restore operation is employed to recover the data of a failed cluster.
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Before starting the restore operation, a snapshot file must be present. It can either be a snapshot file from a previous backup operation, or from a remaining [data directory](https://github.com/coreos/etcd/blob/master/Documentation/op-guide/configuration.md#--data-dir). `datadir` is located at `$DATA_DIR/member/snap/db`. For more information and examples on restoring a cluster from a snapshot file, see [etcd disaster recovery documentation](https://github.com/coreos/etcd/blob/master/Documentation/op-guide/recovery.md#restoring-a-cluster).
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If the access URLs of the restored cluster is changed from the previous cluster, the Kubernetes API server must be reconfigured accordingly. In this case, restart Kubernetes API server with the flag `--etcd-servers=$NEW_ETCD_CLUSTER` instead of the flag `--etcd-servers=$OLD__ETCD_CLUSTER`. Replace `$NEW_ETCD_CLUSTER` and `$OLD__ETCD_CLUSTER` with the respective IP addresses. If a load balancer is used in front of an etcd cluster, you might need to update the load balancer instead.
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If the majority of etcd members have permanently failed, the etcd cluster is considered failed. In this scenario, Kubernetes cannot make any changes to its current state. Although the scheduled pods might continue to run, no new pods can be scheduled. In such cases, recover the etcd cluster and potentially reconfigure Kubernetes API server to fix the issue.
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## Upgrading and rolling back etcd clusters
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### Important assumptions
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The upgrade procedure described in this document assumes that either:
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1. The etcd cluster has only a single node, or
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1. The etcd cluster has multiple nodes. In this case, the upgrade procedure requires shutting down the
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etcd cluster. During the time the etcd cluster is shutdown, the Kubernetes API Server
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will be read only.
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1. The etcd cluster has only a single node
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2. The etcd cluster has multiple nodes.
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In this case, the upgrade procedure requires shutting down the
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etcd cluster. During the time the etcd cluster is shut down, the Kubernetes API Server will be read only.
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**Warning**: Deviations from the assumptions are untested by continuous
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integration, and deviations might create undesirable consequences. Additional
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information about operating an etcd cluster is available [from the etcd
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maintainers](https://github.com/coreos/etcd/tree/master/Documentation).
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integration, and deviations might create undesirable consequences. Additional information about operating an etcd cluster is available [from the etcd maintainers](https://github.com/coreos/etcd/tree/master/Documentation).
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## etcd for Kubernetes: high-level goals
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Access control: Give only kube-apiserver read/write access to etcd. You do not
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want the API server's etcd exposed to every node in your cluster, or worse, to the
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internet at large. Access to etcd is equivalent to root access in your
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cluster.
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Data reliability: For reasonable safety, either etcd needs to be run as a
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[cluster](/docs/admin/high-availability/#clustering-etcd), or etcd's data directory
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should be located on durable storage, for example, a Google Compute Engine persistent disk.
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In either case, if high availability is
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required--as it might be in a production cluster--the data directory ought to be
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[backed up periodically](https://coreos.com/etcd/docs/latest/op-guide/recovery.html)
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to reduce downtime in case of corruption.
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## Background
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### Background
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As of Kubernetes version 1.5.1, we are still using etcd from the 2.2.1 release with
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the v2 API. Also, we have no pre-existing process for updating etcd, as we have
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@ -79,9 +237,9 @@ There are requirements on how an etcd cluster upgrade can be performed. The prim
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#### One minor release at a time
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Upgrade only one minor release at a time. For example, we cannot upgrade directly from 2.1.x to 2.3.x.
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Within patch releases it is possible to upgrade and downgrade between arbitrary versions. Starting a cluster for
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Within patch releases it is possible to upgrade and downgrade between arbitrary versions. Starting a cluster for
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any intermediate minor release, waiting until the cluster is healthy, and then
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shutting down the cluster down will perform the migration. For example, to upgrade from version 2.1.x to 2.3.y,
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shutting down the cluster down will perform the migration. For example, to upgrade from version 2.1.x to 2.3.y,
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it is enough to start etcd in 2.2.z version, wait until it is healthy, stop it, and then start the
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2.3.y version.
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@ -193,7 +351,7 @@ script works as follows:
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in v2 format.
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1. Finally update the contents of the version file.
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## Upgrade procedure
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### Upgrade procedure
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Simply modify the command line in the etcd manifest to:
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1. Run the migration script. If the previously run version is already in the
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