@Zaili Xu
Regarding your queries:
1. Am I supposed to install and run Grafana before create a cluster ?
>>>> No, you do not need to install Grafana (Or AMS separately). Once the cluster is installed then you can install those services anytime you want. Also if you want then you can install AMS/Grafana during the cluster install.
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2. If not is Ambari going to install and configure Grafana using the "Grafana Admin Password" I give me arbitrarily ? How do I know Grafana's Admin Password ?
>>>> Yes, while installing AMS services from Ambari UI it asks for grafana admin password to be entered. That you will need to remember. Else you can use the above link which is shared by @Geoffrey Shelton Okot To reset the grafana admin credentials.
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