--- canonical: "https://safekit.eviden.com/products/high-availability-software-for-application-clustering/power-outage-and-network-isolation-in-a-cluster/" llms_index: "https://safekit.eviden.com/llms.txt" llms_section: "Key Concepts & Educational Content" topics: "Handling Power Outages and Network Isolation in a HA Cluster, SafeKit Proposes a SANless Architecture for Resilient Failover and Split-Brain Prevention, What are the different scenarios in case of network isolation in a cluster?, What are the different scenarios in case of power outage in a cluster?, 🔍 SafeKit High Availability Navigation Hub" --- # Handling Power Outages and Network Isolation in a HA Cluster ## SafeKit Proposes a SANless Architecture for Resilient Failover and Split-Brain Prevention [🧑 Contact us](https://safekit.eviden.com/products/high-availability-software-for-application-clustering/contact-us-for-safekit/) [🎁 SafeKit free trial](https://safekit.eviden.com/products/high-availability-software-for-application-clustering/safekit-free-trial/) [🏅 Free certification](https://training.my.evidian.com/mod/page/view.php?id=712) [💰 Perpetual license cost](https://safekit.eviden.com/products/high-availability-software-for-application-clustering/get-a-quote-safekit-en/) ## What are the different scenarios in case of network isolation in a cluster? ### A single network * ![SafeKit primary secondary](data:image/svg+xml,%3Csvg%20xmlns='http://www.w3.org/2000/svg'%20viewBox='0%200%20300%20169'%3E%3C/svg%3E)![SafeKit primary secondary](https://safekit.eviden.com/wp-content/uploads/2023/02/safekit-prim-second-300.png) * ![SafeKit alone alone](data:image/svg+xml,%3Csvg%20xmlns='http://www.w3.org/2000/svg'%20viewBox='0%200%20300%20169'%3E%3C/svg%3E)![SafeKit alone alone](https://safekit.eviden.com/wp-content/uploads/2023/02/safekit-alone-alone-300.png) When there is a network isolation, the default behavior is: * as heartbeats are lost for each node, each node goes to ALONE and runs the application with its virtual IP address (double execution of the application modifying its local data), * when the isolation is repaired, one ALONE node is forced to stop and to resynchronize its data from the other node, * at the end the cluster is PRIM-SECOND (or SECOND-PRIM according the duplicate virtual IP address detection made by Windows). ### Two networks with a dedicated replication network * ![SafeKit primary secondary](data:image/svg+xml,%3Csvg%20xmlns='http://www.w3.org/2000/svg'%20viewBox='0%200%20300%20169'%3E%3C/svg%3E)![SafeKit primary secondary](https://safekit.eviden.com/wp-content/uploads/2023/02/safekit-prim-second-300.png) * ![SafeKit failover](data:image/svg+xml,%3Csvg%20xmlns='http://www.w3.org/2000/svg'%20viewBox='0%200%20300%20169'%3E%3C/svg%3E)![SafeKit failover](https://safekit.eviden.com/wp-content/uploads/2023/02/safekit-prim-second-300.png) When there is a network isolation, the behavior with a dedicated replication network is: * a dedicated replication network is implemented on a private network, * heartbeats on the production network are lost (isolated network), * heartbeats on the replication network are working (not isolated network), * the cluster stays in PRIM/SECOND state. ### A single network and a splitbrain checker * ![SafeKit primary secondary](data:image/svg+xml,%3Csvg%20xmlns='http://www.w3.org/2000/svg'%20viewBox='0%200%20300%20169'%3E%3C/svg%3E)![SafeKit primary secondary](https://safekit.eviden.com/wp-content/uploads/2023/02/safekit-prim-second-300.png) * ![SafeKit alone wait](data:image/svg+xml,%3Csvg%20xmlns='http://www.w3.org/2000/svg'%20viewBox='0%200%20300%20169'%3E%3C/svg%3E)![SafeKit alone wait](https://safekit.eviden.com/wp-content/uploads/2023/02/safekit-alone-wait-300.png) When there is a network isolation, the behavior with a split-brain checker is: * a split-brain checker has been configured with the IP address of a witness (typically a router), * the split-brain checker operates when a server goes from PRIM to ALONE or from SECOND to ALONE, * in case of network isolation, before going to ALONE, both nodes test the IP address, * the node which can access the IP address goes to ALONE, the other one goes to WAIT, * when the isolation is repaired, the WAIT node resynchronizes its data and becomes SECOND. Note: If the witness is down or disconnected, both nodes go to WAIT and the application is no more running. That's why you must choose a robust witness like a router. ## What are the different scenarios in case of power outage in a cluster? ### Primary node power outage * ![SafeKit primary secondary](data:image/svg+xml,%3Csvg%20xmlns='http://www.w3.org/2000/svg'%20viewBox='0%200%20300%20169'%3E%3C/svg%3E)![SafeKit primary secondary](https://safekit.eviden.com/wp-content/uploads/2023/02/safekit-prim-second-300.png) * ![SafeKit stop alone](data:image/svg+xml,%3Csvg%20xmlns='http://www.w3.org/2000/svg'%20viewBox='0%200%20300%20169'%3E%3C/svg%3E)![SafeKit stop alone](https://safekit.eviden.com/wp-content/uploads/2023/02/safekit-stop-alone-300.png) * ![SafeKit second prim](data:image/svg+xml,%3Csvg%20xmlns='http://www.w3.org/2000/svg'%20viewBox='0%200%20300%20169'%3E%3C/svg%3E)![SafeKit second prim](https://safekit.eviden.com/wp-content/uploads/2023/02/safekit-second-prim-300.png) When a power outage stops only the primary node: * there is an automatic failover on the secondary node, which becomes ALONE and restarts the application, * when node 1 is rebooted, it becomes SEDOND after resynchronization of replicated data, * the roles of primary and secondary can be swapped by an adminsitrator if needed. ### Secondary node power outage * ![SafeKit primary secondary](data:image/svg+xml,%3Csvg%20xmlns='http://www.w3.org/2000/svg'%20viewBox='0%200%20300%20169'%3E%3C/svg%3E)![SafeKit primary secondary](https://safekit.eviden.com/wp-content/uploads/2023/02/safekit-prim-second-300.png) * ![SafeKit alone stop](data:image/svg+xml,%3Csvg%20xmlns='http://www.w3.org/2000/svg'%20viewBox='0%200%20300%20169'%3E%3C/svg%3E)![SafeKit alone stop](https://safekit.eviden.com/wp-content/uploads/2023/02/safekit-alone-stop-300.png) When a power outage stops only the secondary node: * there is no failover, the primary becomes ALONE and the application continues its execution on node 1, * when node 2 is rebooted, it becomes SEDOND after resynchronization of replicated data. ### General power outage - case 1 * ![SafeKit primary secondary](data:image/svg+xml,%3Csvg%20xmlns='http://www.w3.org/2000/svg'%20viewBox='0%200%20300%20169'%3E%3C/svg%3E)![SafeKit primary secondary](https://safekit.eviden.com/wp-content/uploads/2023/02/safekit-prim-second-300.png) * ![SafeKit stop stop](data:image/svg+xml,%3Csvg%20xmlns='http://www.w3.org/2000/svg'%20viewBox='0%200%20300%20169'%3E%3C/svg%3E)![SafeKit stop stop](https://safekit.eviden.com/wp-content/uploads/2023/02/safekit-stop-stop-300.png) * ![SafeKit wait stop](data:image/svg+xml,%3Csvg%20xmlns='http://www.w3.org/2000/svg'%20viewBox='0%200%20300%20169'%3E%3C/svg%3E)![SafeKit wait stop](https://safekit.eviden.com/wp-content/uploads/2023/02/safekit-wait-stop-300.png) When a power outage stops both nodes, the default behavior is: * both nodes goes to STOP, * when node 1 is rebooted, it does not go into ALONE state and does not restart the application because it doesn't know if it has the up-to-date data. So it goes to the WAIT state waiting for the restart of the other node, * when node 2 is rebooted, both nodes return to their previous PRIM/SECOND states. ### General power outage - case 2 * ![SafeKit primary secondary](data:image/svg+xml,%3Csvg%20xmlns='http://www.w3.org/2000/svg'%20viewBox='0%200%20300%20169'%3E%3C/svg%3E)![SafeKit primary secondary](https://safekit.eviden.com/wp-content/uploads/2023/02/safekit-prim-second-300.png) * ![SafeKit stop stop](data:image/svg+xml,%3Csvg%20xmlns='http://www.w3.org/2000/svg'%20viewBox='0%200%20300%20169'%3E%3C/svg%3E)![SafeKit stop stop](https://safekit.eviden.com/wp-content/uploads/2023/02/safekit-stop-stop-300.png) * ![SafeKit alone stop](data:image/svg+xml,%3Csvg%20xmlns='http://www.w3.org/2000/svg'%20viewBox='0%200%20300%20169'%3E%3C/svg%3E)![SafeKit alone stop](https://safekit.eviden.com/wp-content/uploads/2023/02/safekit-alone-stop-300.png) When a power outage stops both nodes, the behavior with syncdelta is : * syncdelta is set for example to 10 minutes in the configuration meaning that start of a node is accepted even if its data is 10 minutes behind the last sync, * when node 1 is rebooted, it goes to ALONE and restarts the application assuming that the restart is done within 10 minutes after the power failure, * when node 2 is rebooted, it becomes SECOND after resynchronization of replicated data, * Note: if node 2 is rebooted the first, then it becomes ALONE and node 1 will become SECOND at its start. ## 🔍 SafeKit High Availability Navigation Hub Explore SafeKit: Features, technical videos, documentation, and free trial | Resource Type | Description | Direct Link | | --- | --- | --- | | **Key Features** | Why Choose SafeKit for Simple and Cost-Effective High Availability? | [See Why Choose SafeKit for High Availability](https://safekit.eviden.com/products/high-availability-software-for-application-clustering/#why-choose-safekit-for-ha "Discover SafeKit features for simple and cost-effective high availability") | | **Use Cases** | Explore How SafeKit Ensures the High Availability of Critical Infrastructure | [See All Use Cases (OEM Software, Edge Servers, SCADA, and more)](https://safekit.eviden.com/products/high-availability-software-for-application-clustering/#safekit-use-cases "Explore SafeKit high availability use cases") | | **Deployment Model** | All-in-One SANless HA: Shared-Nothing Software Clustering | [See SafeKit All-in-One SANless HA](https://safekit.eviden.com/products/high-availability-software-for-application-clustering/#all-in-one-sanless-ha "Learn about all-in-one SANless high availability with shared-nothing software clustering") | | **HA Strategies** | SafeKit: Infrastructure (VM) vs. Application-Level High Availability | [See SafeKit HA & Redundancy: VM vs. Application Level](https://safekit.eviden.com/products/high-availability-software-for-application-clustering/#safekit-ha-redundancy-choices "Compare VM-level redundancy with SafeKit application-level high availability strategies") | | **Technical Specifications** | Technical Limitations for SafeKit Clustering | [See SafeKit High Availability Limitations](https://safekit.eviden.com/products/high-availability-software-for-application-clustering/#safekit-ha-limitations "Technical requirements and limitations for SafeKit application clustering") | | **Proof of Concept** | SafeKit: High Availability Configuration & Failover Demos | [See SafeKit Failover Tutorials](https://safekit.eviden.com/products/high-availability-software-for-application-clustering/#safekit-failover-tutorials "Step-by-step videos on SafeKit high availability, from installation to automated failover") | | **Architecture** | How the SafeKit Mirror Cluster works (Real-Time Replication & Failover) | [See SafeKit Mirror Cluster: Real-Time Replication & Failover](https://safekit.eviden.com/products/high-availability-software-for-application-clustering/#safekit-mirror-cluster "See technical architecture and failover mechanism of SafeKit Mirror Cluster") | | **Architecture** | How the SafeKit Farm Cluster works (Network Load Balancing & Failover) | [See SafeKit Farm Cluster: Network Load Balancing & Failover](https://safekit.eviden.com/products/high-availability-software-for-application-clustering/#safekit-farm-cluster "Technical overview of SafeKit Farm Cluster architecture with network load balancing") | | **Competitive Advantages** | Comparison: SafeKit vs. Traditional High Availability (HA) Clusters | [See SafeKit vs. Traditional HA Cluster Comparison](https://safekit.eviden.com/products/high-availability-software-for-application-clustering/#safekit-ha-comparison "Detailed comparison of SafeKit software vs traditional hardware-based HA clusters") | | **Technical Resources** | SafeKit High Availability: Documentation, Downloads & Trial | [See SafeKit HA Free Trial & Technical Documentation](https://safekit.eviden.com/products/high-availability-software-for-application-clustering/#safekit-ha-technical-resources "Access SafeKit free trial, technical documentation, and high availability white papers") | | **Pre-configured Solutions** | SafeKit Application Module Library: Ready-to-Use HA Solutions | [See SafeKit High Availability Application Modules](https://safekit.eviden.com/products/high-availability-software-for-application-clustering/#safekit-ha-application-modules "Browse the library of pre-configured SafeKit modules for automated application failover") | [🧑 Contact us](https://safekit.eviden.com/products/high-availability-software-for-application-clustering/contact-us-for-safekit/) [🎁 SafeKit free trial](https://safekit.eviden.com/products/high-availability-software-for-application-clustering/safekit-free-trial/) [🏅 Free certification](https://training.my.evidian.com/mod/page/view.php?id=712) [💰 Perpetual license cost](https://safekit.eviden.com/products/high-availability-software-for-application-clustering/get-a-quote-safekit-en/)