solana/docs/src/running-validator/validator-failover.md

---
title: Failover Setup
---

A simple two machine instance failover method is described here, which allows you to:
* upgrade your validator software with virtually no down time, and
* failover to the secondary instance when your monitoring detects a problem with
  the primary instance
without any safety issues that would otherwise be associated with running two
instances of your validator.

You will need two validator-class machines for your primary and secondary
validator. A third machine for running an [etcd](https://etcd.io/) cluster,
which is used to store the tower voting record for your validator.

## Setup

### etcd cluster setup

There is ample documentation regarding etcd setup and configuration at
https://etcd.io/, please generally familiarize yourself with etcd before
continuing.

It's recommended that etcd be installed on a separate machine from your primary
and secondary validator machines. This machine must be highly available, and
depending on your needs you may wish to configure etcd with more than just
one node.

First install `etcd` as desired for your machine. Then TLS certificates must be
created for authentication between the etcd cluster and your validator.  Here is
one way to do this:

With [Golang](https://golang.org/) installed, run `go get
github.com/cloudflare/cfssl/cmd/cfssl`.  The `cfssl` program should now be
available at `~/go/bin/cfssl`.  Ensure `~/go/bin` is in your PATH by running
`PATH=$PATH:~/go/bin/`.

Now create a certificate directory and configuration file:
```
mkdir -p certs/
echo '{"CN":"etcd","hosts":["localhost", "127.0.0.1"],"key":{"algo":"rsa","size":2048}}' > certs/config.json
```

then create certificates for the etcd server and the validator:
```
cfssl gencert -initca certs/config.json | cfssljson -bare certs/etcd-ca
cfssl gencert -ca certs/etcd-ca.pem -ca-key certs/etcd-ca-key.pem certs/config.json | cfssljson -bare certs/validator
cfssl gencert -ca certs/etcd-ca.pem -ca-key certs/etcd-ca-key.pem certs/config.json | cfssljson -bare certs/etcd
```

Copy these files to your primary and secondary validator machines:
* `certs/validator-key.pem`
* `certs/validator.pem`
* `certs/etcd-ca.pem`

and these files to the machine running the etcd server:
* `certs/etcd.pem`
* `certs/etcd-key.pem`
* `certs/etcd-ca.pem`

With this configuration, both the validator and etdc will share the same
TLS certificate authority and will each authenticate the other with it.


Start `etcd` with the following arguments:
```bash
etcd --auto-compaction-retention 2 --auto-compaction-mode revision \
  --cert-file=certs/etcd.pem --key-file=certs/etcd-key.pem \
  --client-cert-auth \
  --trusted-ca-file=certs/etcd-ca.pem \
  --listen-client-urls=https://127.0.0.1:2379 \
  --advertise-client-urls=https://127.0.0.1:2379
```

and use `curl` to confirm the etcd TLS certificates are properly configured:
```bash
curl --cacert certs/etcd-ca.pem https://127.0.0.1:2379/ --cert certs/validator.pem --key certs/validator-key.pem
```
On success, curl will return a 404 response.

For more information on etcd TLS setup, please refer to
https://etcd.io/docs/v3.5/op-guide/security/#example-2-client-to-server-authentication-with-https-client-certificates

### Primary Validator
The following additional `solana-validator` parameters are required to enable
tower storage into etcd:

```
solana-validator ... \
  --tower-storage etcd \
  --etcd-cacert-file certs/etcd-ca.pem \
  --etcd-cert-file certs/validator.pem \
  --etcd-key-file certs/validator-key.pem \
  --etcd-endpoint 127.0.0.1:2379  # <-- replace 127.0.0.1 with the actual IP address
```

Note that once running your validator *will terminate* if it's not able to write
its tower into etcd before submitting a vote transactioin, so it's essential
that your etcd endpoint remain accessible at all times.

### Secondary Validator
Configure the secondary validator like the primary with the exception of the
following `solana-validator` command-line argument changes:
* Generate and use a secondary validator identity: `--identity secondary-validator-keypair.json`
* Add `--no-check-vote-account`
* Add `--authorized-voter validator-keypair.json` (where
  `validator-keypair.json` is the identity keypair for your primary validator)

## Triggering a failover manually
When both validators are running normally and caught up to the cluster, a
failover from primary to secondary can be triggered by running the following
command on the secondary validator:
```bash
$ solana-validator wait-for-restart-window --identity validator-keypair.json \
  && solana-validator set-identity validator-keypair.json
```

The secondary validator will acquire a lock on the tower in etcd to ensure
voting and block production safely switches over from the primary validator.

The primary validator will then terminate as soon as it detects the secondary
validator using its identity.

Note: When the primary validator restarts (which may be immediate if you have
configured your primary validator to do so) it will reclaim its identity
from the secondary validator. This will in turn cause the secondary validator to
exit. However if/when the secondary validator restarts, it will do so using the
secondary validator identity and thus the restart cycle is broken.

## Triggering a failover via monitoring
Monitoring of your choosing can invoke the `solana-validator set-identity
validator-keypair.json` command mentioned in the previous section.

It is not necessary to guarantee the primary validator has halted before failing
over to the secondary, as the failover process will prevent the primary
validator from voting and producing blocks even if it is in an unknown state.

## Validator Software Upgrades
To perform a software upgrade using this failover method:
1. Install the new software version on your primary validator system but do not
   restart it yet.
2. Trigger a manual failover to your secondary validator. This should cause your
   primary validator to terminate.
3. When your primary validator restarts it will now be using the new software version.
4. Once the primary validator catches up upgrade the secondary validator at
   your convenience.