Palo has a very simple and elegant system architecture. Its core components only include two kinds of components, one with state, one with no state which is optional. When using the Palo service hosted by Baidu AI cloud, an extra front-end console is required for some cluster management operations.

Architecture diagram

As shown in the above figure, the middle part is the core component of Palo, mainly including the following modules:

1. Leader Node

   Leader Node is also called Frontend（FE）. In other documents, both of the names refer to the same componnet. The Leader Node is mainly used for accessing the connection requested by users, storage and management of metadata, parsing of query statements and generation of query plans, management of the cluster nodes status, as well as the tasks scheduling submitted by various users and within the system.

   The Leader Node has built-in MySQL protocol layer and Http Server. Users can choose different protocols to connect to the Leader Node depending on specific operation. At the same time, the Leader Node also has a built-in UI interface. Users can click the Palo UI button at the upper right corner of the front console page to enter.

   Generally, one Palo cluster has 1 or 3 Leader Nodes. When the number is 3, Leader Node will automatically form a node group to secure the high availability of components.

2. Compute Node

   Compute Node is also called Backend (BE). In other documents, both of the names refer to the same component. Compute Node is mainly used for the execution of query plan and the storage and management of data. Compute Node can be composed of one or more nodes, and the overall computing power and storage capacity of Palo cluster are in direct proportion to the number of of Compute Node.

   Leader Node interacts with Compute Node through RPC.

3. Broker

   Broker is a stateless process that helps Palo to access the external data source by means of Unix-like file system interface, for example, the data on BOS or HDFS and apply them in data import or export operations.

   In the Palo cluster hosted by Baidu AI cloud, this component will be installed by default. You can view it by executing the SHOW BROKER command after connecting to MySQL protocol by using the MySQL protocol. When in privatization deployment scenario, this component can be an optional component.