Validator Guide: Setup Node Failover
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 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 installed, run
go install github.com/cloudflare/cfssl/cmd/cfssl@latest
. 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:
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:
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 openos-validator
parameters are required to enable
tower storage into etcd:
openos-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 transaction, 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 openos-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
(wherevalidator-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:
$ openos-validator wait-for-restart-window --identity validator-keypair.json \
&& openos-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 openos-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:
- Install the new software version on your primary validator system but do not restart it yet.
- Trigger a manual failover to your secondary validator. This should cause your primary validator to terminate.
- When your primary validator restarts it will now be using the new software version.
- Once the primary validator catches up upgrade the secondary validator at your convenience.