A method of using a plurality of nodes (305-350, 605, 630, 670) to provide network security functionality to a plurality of clients, each node storing a set of operational data required to accomplish said network security functionality, the method comprising: for each node of the plurality of nodes, allocating the node to at least two different replication groups of a plurality of replication groups (360-370, 520, 530) of nodes, the number of nodes in each replication group of the plurality of replication groups being equal to or below a predetermined limit, each replication group of the plurality of replication groups having allocated at least two nodes of the plurality of nodes; and for each node of the plurality of nodes, synchronizing the set of operational data stored in the node within its allocated replication groups only, wherein each node of the plurality of nodes is of one of a number of different node types, said different node types including one or more of: a security node type being a type of nodes dedicated to apply one or more security mechanisms to protect at least one client of the plurality of clients against an unauthorized access, denial of access, misuse, or modification of the client or of a computing resource in a computer network to which the client is connected, each node of said security node type having a communication interface to said computer network; a traffic steering node type being a type of nodes dedicated to control the communication traffic to and from at least one of said plurality of clients, each node of said traffic steering node type having a communication interface to at least one of said plurality of clients; and a middleware node type being a type of nodes dedicated to provide an interface to an operator allowing the operator to set or change configuration parameters that are taken into account by one or more node of the security node type or traffic steering node type, wherein the method further comprises: changing the node type of at least one node of the plurality of nodes from one of the number of node types to a different one of the number of node types. for each node of the plurality of nodes, allocating the node to at least two different replication groups of a plurality of replication groups (360-370, 520, 530) of nodes, the number of nodes in each replication group of the plurality of replication groups being equal to or below a predetermined limit, each replication group of the plurality of replication groups having allocated at least two nodes of the plurality of nodes; and for each node of the plurality of nodes, synchronizing the set of operational data stored in the node within its allocated replication groups only, wherein each node of the plurality of nodes is of one of a number of different node types, said different node types including one or more of: a security node type being a type of nodes dedicated to apply one or more security mechanisms to protect at least one client of the plurality of clients against an unauthorized access, denial of access, misuse, or modification of the client or of a computing resource in a computer network to which the client is connected, each node of said security node type having a communication interface to said computer network; a traffic steering node type being a type of nodes dedicated to control the communication traffic to and from at least one of said plurality of clients, each node of said traffic steering node type having a communication interface to at least one of said plurality of clients; and a middleware node type being a type of nodes dedicated to provide an interface to an operator allowing the operator to set or change configuration parameters that are taken into account by one or more node of the security node type or traffic steering node type, wherein the method further comprises: changing the node type of at least one node of the plurality of nodes from one of the number of node types to a different one of the number of node types. a security node type being a type of nodes dedicated to apply one or more security mechanisms to protect at least one client of the plurality of clients against an unauthorized access, denial of access, misuse, or modification of the client or of a computing resource in a computer network to which the client is connected, each node of said security node type having a communication interface to said computer network; a traffic steering node type being a type of nodes dedicated to control the communication traffic to and from at least one of said plurality of clients, each node of said traffic steering node type having a communication interface to at least one of said plurality of clients; and a middleware node type being a type of nodes dedicated to provide an interface to an operator allowing the operator to set or change configuration parameters that are taken into account by one or more node of the security node type or traffic steering node type, wherein the method further comprises: changing the node type of at least one node of the plurality of nodes from one of the number of node types to a different one of the number of node types.