Cluster
webPDF supports setting up a cluster, i.e., a network of multiple servers that work together to increase data throughput and the availability of web services.
Please note that setting up and configuring a cluster requires a comprehensive understanding of the subject in relation to IT infrastructure, installation and configuration of a cluster in general. This also applies to the installation, configuration and operation of webPDF.
Definition
A cluster is a group of redundant servers that continue to provide uninterrupted service within the cluster in the event of a failure of a single server. Therefore, a cluster always consists of at least two servers. The cluster has a unique name.
A separate license is required to operate the cluster, which licenses a minimum of two servers and also defines the maximum number of servers allowed in the cluster.
A single server in a cluster is called a node. Each node in the cluster has a unique name.
The role defines the node's function in the cluster. The roles in the cluster are coordinator and member. Regardless of their role, all nodes provide the same functions, i.e. the web services, in the cluster.
A coordinator controls the cluster and provides the central configuration for all nodes. All nodes must have exactly the same configuration, which is synchronized from the coordinator to the member.
A member has no special task in the cluster and only provides the functions, i.e. the web services.
Each node has a state that defines, for example, whether it is part of the cluster or whether it can answer requests.
Access to a cluster must always be controlled by a gateway, a load balancer or proxy, which distributes the requests to the nodes of a cluster according to their availability. This central gateway is responsible for failover and load distribution in the cluster.
webPDF itself has no mechanism for distributing requests, i.e. this must be done by third-party software (e.g. a firewall or load balancer).
A Redis storage (as an in-memory cache) is required for the common storage of the session and the document information, which can be used by all nodes. This session storage must be provided and configured (before installation).
The Redis instance is not part of webPDF and must be provided externally.
For the physical file storage, a common file storage must be provided that can be used by all nodes of the cluster. This can be, for example, a share on a NAS (network attached storage) with the NFS (Network File System) or SMB (Server Message Block) protocol, or an S3-compatible object storage.
The shared file storage must be provided externally. It must be a storage that allows parallel access.
It is recommended to build the cluster on the basis of Docker containers.
Information about the cluster and the nodes involved can be accessed at any time via the admin portal under cluster information.
The installation and configuration of the cluster is described in the following documents.