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Virtual IP address
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A virtual IP address (VIP address or VIPA) is an IP address that does not correspond to a single physical network interface. Uses for VIPs include network address translation (especially one-to-many NAT), fault tolerance, and mobility.
Usage
[edit]For one-to-many NAT, a VIP address is advertised from the NAT device (often a router), and incoming data packets destined to that VIP address are routed to different actual IP addresses (with address translation). These VIP addresses have several variations and implementation scenarios, including Common Address Redundancy Protocol (CARP) and Proxy ARP.[1] In addition, if there are multiple actual IP addresses, load balancing can be performed as part of NAT.
VIP addresses are also used for connection redundancy by providing alternative fail-over options for one machine. For this to work, the host has to run an interior gateway protocol like Open Shortest Path First (OSPF) and appear as a router to the rest of the network. It advertises virtual links connected via itself to all of its actual network interfaces. If one network interface fails, normal OSPF topology reconvergence will cause traffic to be sent via another interface.[2][3]
A VIP address can be used to provide nearly unlimited mobility. For example, if an application has an IP address on a physical subnet, that application can be moved only to a host on that same subnet. VIP addresses can be advertised on their own subnet,[a] so its application can be moved anywhere on the reachable network without changing addresses.[2]
Notes
[edit]- ^ This typically accomplished using a full netmask, 32-bits for IPv4 and 128 bits for IPv6, such that the subnet and VIP address are the same and there is just the single VIP address in the subnet.
References
[edit]- ^ "What is a VIP?". Juniper Networks. Retrieved 2017-10-14.
- ^ a b "Virtual IP Address Benefits". Novell. Retrieved 2017-10-14.
- ^ "What is virtual IP address?". Webopedia. 11 August 2005. Retrieved 2017-10-14.
Virtual IP address
View on Grokipediafrom Grokipedia
A virtual IP address (VIP) is an IP address that does not correspond directly to a single physical network interface but is instead associated with a logical or virtual entity, such as a virtual router or a cluster of servers, enabling shared access across multiple devices without tying to specific hardware.[1] This abstraction allows the VIP to "float" between systems, providing a stable endpoint for clients while the underlying infrastructure can change dynamically.[2]
Virtual IP addresses are primarily employed to enhance high availability (HA) and redundancy in networked environments, where a failure in one device must not disrupt service continuity.[1] In HA clustering, for instance, the VIP is assigned to an active node and automatically migrates to a backup node during failover, ensuring that client applications continue connecting via the same address without reconfiguration.[2] Protocols like the Virtual Router Redundancy Protocol (VRRP) define a virtual router using a VIP alongside a virtual router identifier (VRID), where one router acts as the master to forward packets destined for the VIP, while backups monitor and take over if the master fails.[1] This setup eliminates single points of failure in default gateway configurations, supporting IPv4 addresses (VRRPv2) and IPv6 addresses (VRRPv3).[1][3]
Beyond redundancy, VIPs play a crucial role in load balancing, distributing incoming traffic across multiple backend servers to optimize performance and resource utilization.[4] Load balancers expose a VIP as the entry point for client requests, which are then routed to a pool of real servers based on algorithms considering factors like server health or capacity.[4] In IP failover scenarios, such as those using Keepalived with VRRP, VIPs are monitored across cluster nodes and reassigned to healthy ones if a service becomes unreachable, often checking specific ports like 80 for availability.[5]
The implementation of VIPs often involves techniques like IP aliasing on network interfaces or multicast advertisements for election processes, ensuring fault tolerance and scalability in data centers, cloud environments, and enterprise networks.[1] By abstracting the physical topology, VIPs enable seamless scaling, such as adding servers to a cluster without altering client-side DNS or routing tables.[4]
This assigns the address without altering physical interfaces, ensuring it responds to ARP requests when active.[26] Keepalived configuration files specify the VIP, group ID, priority, and advertisement interval in sections like
This sets the group ID to 1, assigns the VIP, raises priority to 110, adjusts the hello interval to 1 second (hold time 3 seconds), and enables preemption.[28] For VRRP, similar commands apply:
Fundamentals
Definition
A virtual IP address (VIP), also known as a VIPA, is an IP address that does not correspond to a single physical network interface but is instead dynamically assigned or shared among multiple interfaces or devices, enabling it to serve as a logical endpoint for network traffic.[6] This abstraction allows the VIP to act as a stable address for services, even as underlying hardware changes, and is commonly managed through protocols that facilitate its migration.[1] Unlike static IP addresses, which are fixed to a specific device or interface, or dynamic IP addresses assigned temporarily via mechanisms like DHCP, virtual IP addresses function as floating logical entities that can be reassigned between hosts or interfaces without disrupting connectivity.[7] This "floating" capability distinguishes VIPs by prioritizing resilience and shared access over direct hardware binding, supporting scenarios where multiple nodes collaborate to maintain service availability.[8] In IPv4 networks, a virtual IP address is a 32-bit value, following the standard addressing format defined in the Internet Protocol specification.[9] For IPv6, it is a 128-bit address, typically configured with the subnet prefix (e.g., /64) of the shared network, though /128 may be used in specific scenarios like point-to-point or VPN configurations.[10][3] The concept of virtual IP addresses emerged in the 1990s, coinciding with the rise of early load balancing and clustering technologies aimed at scaling web applications and improving network reliability amid growing internet traffic.[11] This development was formalized in standards like the Virtual Router Redundancy Protocol (VRRP), first specified in 1998, which introduced mechanisms for sharing VIPs among routers.Key Characteristics
Virtual IP addresses (VIPs) are not tied to any specific physical network interface or hardware device, existing instead within software or firmware layers of networking equipment. This non-physical binding enables flexibility in deployment, as the VIP can be associated with virtual routers or load balancers rather than dedicated hardware ports. In protocols like VRRP, the master router responds to Address Resolution Protocol (ARP) requests for the VIP using a virtual MAC address, allowing multiple devices in a redundancy group to share responsibility for the address without a fixed physical association.[12] A defining trait of VIPs is their support for dynamic reassignment across nodes, facilitating high availability by migrating the active role without interrupting ongoing network traffic. During failover or interface activation, the assuming device issues gratuitous ARP requests to broadcast the updated IP-to-MAC mapping, prompting neighboring hosts to refresh their ARP caches and redirect traffic seamlessly. This mechanism ensures minimal downtime, as the transition occurs at the data link layer without requiring client-side reconfiguration.[13] VIPs provide transparency to end clients, who perceive the address as a singular, reliable endpoint regardless of the underlying infrastructure changes. Clients direct traffic to the VIP as if it were a conventional IP, with the backend system—such as a cluster of routers—handling the distribution or failover invisibly, thereby concealing the complexity of redundancy setups. This abstraction simplifies network management and enhances user experience by maintaining consistent connectivity.[14] The scope and visibility of VIPs vary by deployment, typically limited to local area networks (LANs) where they are resolved via local broadcast protocols like ARP, but extendable to wide area networks (WANs) through advertisement in routing protocols. In LAN contexts, the VIP operates within a shared segment, advertised via multicast advertisements to group members. For global reach, such as in cloud environments, VIPs can be announced using protocols like BGP to propagate routes across distributed networks, enabling broader accessibility without physical constraints.[15][16]Technical Foundations
Underlying Protocols
Virtual IP addresses are primarily enabled through redundancy protocols that facilitate the dynamic assignment and failover of shared IP addresses among multiple network devices. The Virtual Router Redundancy Protocol (VRRP), defined in RFC 3768 and updated in RFC 5798, operates an election mechanism to select a master router responsible for owning the VIP from a group of VRRP routers on a local area network (LAN).[1][17] Backup routers monitor the master's status by exchanging periodic multicast hello advertisements sent to the IPv4 multicast address 224.0.0.18 with a time-to-live (TTL) of 255, ensuring communication remains link-local.[18] The election prioritizes routers based on an 8-bit priority value ranging from 1 to 255, with a default of 100 for non-owner routers; the highest-priority router (or the IP address owner with priority 255) assumes the master role, enabling seamless failover if the master fails.[19] The Hot Standby Router Protocol (HSRP), a proprietary protocol developed by Cisco Systems, provides similar functionality to VRRP but employs UDP-based multicast messages to group address 224.0.0.2 on port 1985 for heartbeat communications among participating routers.[20] Like VRRP, HSRP elects an active router to handle VIP traffic, with standby routers ready to take over based on priority; it assigns a virtual MAC address in the format 0000.0c07.acXX, where XX represents the hexadecimal group number, allowing hosts to ARP for the VIP without disruption during failover.[21] The Common Address Redundancy Protocol (CARP), an open-source variant originally implemented in OpenBSD, extends VRRP-like redundancy to multiple hosts sharing IP addresses, ensuring continuous availability even if individual hosts fail.[22] CARP uses protocol number 112 for its packets and authenticates advertisements with symmetric keys via an SHA1-HMAC mechanism, where a shared password protects against spoofing and must be identically configured across all group members for secure operation.[23] While not a traditional redundancy protocol, IP anycast relates to virtual IP concepts by enabling global load distribution, where multiple nodes advertise the same IP address via the Border Gateway Protocol (BGP), allowing routers to forward traffic to the nearest instance based on BGP's path selection metrics.[24] In larger networks, virtual IPs from protocols like VRRP or HSRP can be advertised using extensions in interior gateway protocols such as Open Shortest Path First (OSPF) or exterior protocols like BGP; the master router treats the VIP as a connected route and redistributes it into these protocols to propagate reachability beyond the local LAN.[20]Configuration Basics
Configuring a virtual IP (VIP) address involves assigning it to a loopback or virtual interface on participating devices and enabling a redundancy protocol such as VRRP or HSRP to manage failover.[3] The process begins by selecting a shared VIP within the subnet of the physical interfaces, then configuring the protocol parameters including a group identifier to group routers, priority values to determine the master (higher priority wins, default 100), and advertisement timers typically set to around 1 second for prompt failure detection.[25] Preemption is often enabled by default, allowing a higher-priority device to reclaim the master role upon recovery, though a delay can be configured to avoid flapping.[3] In Linux environments, a VIP can be statically assigned to the loopback interface using theip command for basic setups, or dynamically managed via tools like Keepalived for VRRP implementation. For example, to add a VIP to the loopback device:
ip addr add 192.0.2.1/32 dev lo
ip addr add 192.0.2.1/32 dev lo
vrrp_instance, starting the service with systemctl start keepalived.[27]
On Cisco IOS devices, configuration occurs in interface mode for protocols like HSRP or VRRP. For HSRP, enter the interface and use commands such as:
standby 1 ip 192.0.2.1
standby 1 priority 110
standby 1 timers 1 3
standby 1 preempt
standby 1 ip 192.0.2.1
standby 1 priority 110
standby 1 timers 1 3
standby 1 preempt
vrrp 1 ip 192.0.2.1 followed by priority and timer adjustments.[25]
Monitoring relies on periodic keepalive advertisements or heartbeats sent by the master device; backups listen for these, declaring master down after the master down interval (typically 3 times the advertisement interval plus skew time).[3] Interface tracking can decrement priority if a monitored link fails, triggering failover.[28]
For IPv6 environments, VRRP uses link-local addresses for advertisements (multicast to FF02::12) and supports global unicast VIPs, ensuring compatibility with Stateless Address Autoconfiguration (SLAAC) by avoiding conflicts in router advertisements.[3] The first configured IPv6 address on the interface must be link-local to form valid VRRP packets.[3]
Applications
Load Balancing
In load balancing, a virtual IP (VIP) address serves as the frontend endpoint for incoming traffic, allowing a load balancer to distribute requests across multiple backend real servers to optimize performance and resource utilization. The VIP acts as a single, unified entry point that clients address, while the load balancer maps these requests to real server IPs either through network address translation (NAT), where the load balancer rewrites source or destination addresses, or direct routing methods like direct server return, in which responses bypass the load balancer. This setup enables efficient traffic distribution at layers 4 through 7 of the OSI model, supporting both transport-level and application-level balancing.[29][30][31] Layer 4 load balancing, operating at the transport layer, uses the VIP to route traffic based on TCP or UDP port information, along with source and destination IP addresses, without inspecting packet contents. This approach is efficient for non-HTTP protocols and high-volume scenarios, as it performs simple packet-level decisions. In contrast, Layer 7 load balancing, at the application layer, examines higher-level data such as HTTP headers, URLs, or cookies through the VIP, enabling content-aware routing decisions like directing specific requests to specialized servers. The choice between these layers depends on the need for speed in Layer 4 versus intelligent distribution in Layer 7, with the VIP remaining the common ingress point in both.[32][33] Practical implementations often leverage VIPs in conjunction with established techniques. Hardware appliances like the F5 BIG-IP system use VIP pools, where multiple virtual servers share a VIP to manage traffic to pooled real servers, supporting advanced algorithms for equitable load spreading.[29] By distributing traffic via VIPs, load balancing enhances overall system metrics, such as increasing throughput by parallelizing requests across servers and reducing average latency through optimized path selection and resource contention avoidance. To maintain session integrity in stateful applications, persistence mechanisms tie subsequent requests from the same client to the initial server using methods like cookie insertion, which embeds server identifiers in HTTP responses, or source IP hashing, which generates a consistent hash from the client's IP to select the backend. These features ensure reliable performance scaling without disrupting user sessions.[34][35][32][36]High Availability and Failover
Virtual IP addresses (VIPs) are essential for high availability (HA) configurations, enabling seamless redundancy by allowing a shared IP to migrate between nodes without disrupting client connections. In HA setups, the VIP serves as a stable endpoint for services, with one active node owning it while backups monitor for failures. Upon detecting an outage, the VIP is reassigned to a healthy node, minimizing downtime and ensuring continuous service access.[3] The failover process begins when the active (master) node fails, triggering backups to detect the absence of periodic advertisements or heartbeats. The backup with the highest priority then assumes the VIP, broadcasting a gratuitous Address Resolution Protocol (ARP) message to update network switches and hosts with the new MAC address mapping for the VIP. This reassignment occurs rapidly; in modern implementations supporting sub-second advertisement intervals, failover can complete in under one second, preventing packet loss.[3][37] Protocols like the Virtual Router Redundancy Protocol (VRRP) and Hot Standby Router Protocol (HSRP) standardize this behavior. In VRRP, master election uses priority values (default 100, up to 255 for the IP owner), with the master sending periodic advertisements; failure of the Master_Down_Interval prompts the highest-priority backup to transition and send gratuitous ARPs. HSRP employs active/standby states, where the active router sends hello messages, and standby routers monitor for misses before preempting with the VIP via gratuitous ARP if configured. Both protocols ensure transparent failover, with HSRP allowing configurable hello intervals as low as 50 milliseconds for faster detection.[3][37] In clustering environments, such as server farms, VIPs migrate between active and passive nodes to maintain service continuity. For instance, in database systems like MySQL replication, the VIP points clients to the primary replica; upon failure, it shifts to a secondary node after promotion, using tools like Heartbeat or Keepalived for management. This active/passive model supports applications requiring fault tolerance, with heartbeats exchanged at intervals of 1-3 seconds to balance quick failure detection against false positives from transient network issues.[38][39] These mechanisms contribute to high uptime targets, such as 99.99% availability (about 52 minutes of annual downtime), by automating recovery and reducing mean time to recovery in HA clusters.[40]Network Address Translation
In Network Address Translation (NAT), a virtual IP address (VIP) serves as a public-facing IP that enables connectivity between private internal networks and external networks, often functioning as a gateway for address mapping. One-to-many NAT configurations utilize a single VIP to map incoming traffic to multiple internal private IP addresses, allowing the router or firewall to direct packets based on criteria such as ports or application types. For instance, in destination NAT (DNAT), the device responds to Address Resolution Protocol (ARP) requests for the VIP using Proxy ARP, ensuring that external traffic destined for the VIP is intercepted and translated to the appropriate internal host without requiring the internal devices to have direct public exposure.[41][42] Port Address Translation (PAT), a common variant of many-to-one NAT, employs a single VIP—typically the router's external interface IP—to handle outbound traffic from multiple internal devices by multiplexing connections using unique port numbers. This approach conserves public IP addresses by translating source IPs and ports for outgoing packets and reversing the process for responses, preventing port exhaustion in scenarios with numerous internal clients. In contrast, inbound NAT often relies on static mappings for servers, where a dedicated VIP is fixed to a specific internal IP for services like web hosting, while dynamic mappings support client devices initiating connections.[43][41] Practical examples include home routers, where the WAN IP acts as a VIP for PAT, enabling all household devices to share a single public address for internet access. In enterprise environments, firewalls such as those from Palo Alto Networks configure one-to-many DNAT rules to route traffic from a single VIP to internal servers based on application protocols, for example, directing HTTP requests to a web server at 10.1.1.100 and SSH to 10.1.1.101. These setups enhance security by hiding internal topologies and can integrate with redundancy mechanisms for failover in NAT operations.[44][43]Mobility Support
Virtual IP addresses play a crucial role in enabling mobility support by allowing devices to maintain a consistent network identity during transitions between different access points or networks. In roaming scenarios, such as when mobile hosts like laptops switch from Wi-Fi to cellular connections, the virtual IP serves as a stable endpoint identifier that remains unchanged, while the underlying physical IP (care-of address) updates dynamically. This is achieved through protocols like Mobile IP, where the home agent tunnels traffic to the device's current location, ensuring seamless connectivity without disrupting ongoing sessions.[45] In virtual private networks (VPNs), virtual IPs are assigned to client tunnels, providing a fixed address within the corporate network regardless of the user's physical location or local ISP assignment. This assignment occurs via a virtual adapter on the client device, which overlays the VPN IP independently of the local network interface, facilitating secure and consistent access to resources as users roam between home, office, or public networks. For instance, in enterprise wireless environments, virtual IPs assigned through mobility controllers allow user sessions to persist across access points and subnets, supporting applications like VoIP without reconnection. Similarly, for IoT devices migrating between subnets—such as sensors moving within a smart factory—virtual IPs enable uninterrupted data flows by abstracting the physical network changes.[46][45] These mechanisms address key challenges in mobile networking, such as frequent DNS updates, which are reduced because the virtual IP remains static and resolvable without reconfiguration. TCP connections are preserved through techniques like binding updates and keepalives, where the home agent maintains session state and forwards packets transparently, preventing disruptions from network-layer changes. Protocol advertisements, such as those in Proxy Mobile IP, further enhance this by decoupling the mobile node's identity from its locator, supporting efficient handovers in large-scale deployments.Implementations
Hardware-Based
Hardware-based virtual IP (VIP) implementations leverage dedicated physical networking devices, such as routers, Layer 3 switches, and specialized appliances, to provide redundancy, load distribution, and high availability through protocols like Hot Standby Router Protocol (HSRP) and Virtual Router Redundancy Protocol (VRRP). These setups utilize hardware-specific features for efficient processing, including support for aggregated interfaces to enhance bandwidth and fault tolerance while advertising VIPs via routing protocols for network-wide reachability.[47][48] In router configurations, devices from vendors like Cisco and Juniper support VIPs on aggregated interfaces, such as EtherChannel (LAG) groups in Cisco IOS or aggregated Ethernet interfaces in Junos OS, allowing multiple physical links to operate as a single logical interface for the VIP. This setup enables the VIP to serve as a shared gateway IP across the bundle, with the active router responding to ARP requests using a virtual MAC address. OSPF is commonly used to advertise routes associated with the VIP, ensuring dynamic propagation of the virtual endpoint to other network devices without manual static route configuration. For example, in Cisco routers, HSRP groups on LAG interfaces maintain the VIP's availability during link failures, while Juniper's VRRP on AE interfaces supports similar redundancy with OSPF integration for route advertisement.[49][50][51] At the switch level, Layer 3 switches employ HSRP groups to manage VIPs, where multiple switches share a virtual IP and MAC address on VLAN interfaces or SVIs, enabling seamless failover for end hosts. Cisco Catalyst and Nexus series switches, for instance, configure HSRP groups with a designated VIP that the active switch owns, responding to client traffic while backups monitor via hello packets. Juniper's Virtual Chassis technology extends this by allowing multiple interconnected switches to function as a single logical device, sharing VIPs across the chassis via VRRP; this eliminates the need for inter-switch trunks for redundancy and simplifies management of the shared VIP pool.[52][47][53][48] Load balancing appliances, such as Citrix NetScaler (now part of Citrix ADC), assign VIPs directly to virtual servers, acting as the frontend IP for incoming client connections while distributing traffic to backend real servers based on configured policies. In this hardware-accelerated environment, a VIP is bound to one or more load balancing virtual servers, each handling specific protocols like HTTP or TCP, with the appliance using ARP to announce the VIP's MAC address to the network. High-end NetScaler models support clustering for shared VIP management across multiple appliances, ensuring continuity during hardware failures.[54][55] Performance in hardware-based VIPs benefits from specialized acceleration, particularly for ARP handling, where devices offload resolution and response generation to ASICs, reducing CPU overhead and enabling low-latency failover. Cisco switches, for example, use hardware acceleration in Dynamic ARP Inspection (DAI) to validate and process ARP packets for HSRP VIPs at line rate. Similarly, Juniper and Citrix hardware employs dedicated forwarding engines to manage ARP broadcasts for VIPs efficiently. These implementations scale to support thousands of VIPs per device in enterprise and data center environments, depending on the model; for instance, Cisco Nexus platforms handle hundreds of HSRP groups per switch depending on the model and configuration, while high-end Citrix ADC MPX appliances support thousands of virtual servers and associated VIPs depending on licensing and model.[56][57][47][58][59]Software-Based
Software-based virtual IP (VIP) implementations leverage operating system tools and open-source software to manage VIPs for high availability and load distribution without dedicated hardware. These solutions typically involve daemons or services that monitor node health and dynamically assign VIPs to active hosts, ensuring seamless failover. In Linux and Unix environments, Keepalived is a widely used daemon that implements the Virtual Router Redundancy Protocol (VRRP) to manage VIPs across multiple nodes.[60] It operates by electing a master node based on priority and VRRP advertisements, assigning the VIP to the master's network interface while backups remain on standby.[27] Configuration occurs via the/etc/keepalived/keepalived.conf file, where sections define the VRRP instance, including the VIP address (e.g., 192.168.122.200/24), interface (e.g., eth0), virtual router ID (VRID, e.g., 51), and authentication for secure advertisements.[27] Upon master failure, detected through missed VRRP packets, the backup node preemptively or non-preemptively assumes the VIP within seconds, supporting both failover and load balancing via integration with Linux Virtual Server (LVS).[60] Installation is straightforward using package managers like yum install keepalived on Red Hat-based systems, followed by enabling the service.[27]
Another key tool in Linux clusters is Pacemaker, a resource manager that oversees VIP assignment in conjunction with Corosync for cluster communication.[61] It treats VIPs as resources using Open Cluster Framework (OCF) agents like ocf:heartbeat:IPaddr2, which handles addition and removal of the VIP on specified nodes via the ip command.[61] Configuration involves defining primitives in XML, such as specifying the IP address, CIDR netmask, and network interface (e.g., <primitive id="vip1" class="ocf" provider="heartbeat" type="IPaddr2"><instance_attributes id="vip1-params"><nvpair id="vip1-ip" name="ip" value="192.168.1.100"/><nvpair id="vip1-cidr" name="cidr_netmask" value="24"/><nvpair id="vip1-iface" name="nic" value="eth0"/></instance_attributes></primitive>), along with monitoring intervals (e.g., every 30 seconds).[61] Pacemaker enforces constraints like location rules to prefer certain nodes (e.g., <rsc_location id="loc-vip1" rsc="vip1" node="node1" score="200"/>), enabling automatic failover based on node health and quorum.[61] This setup integrates with broader cluster resources, such as databases or services, for comprehensive high availability.
On Windows platforms, Network Load Balancing (NLB) provides software-based VIP management across cluster nodes, treating multiple servers as a single virtual cluster.[62] NLB assigns a shared cluster IP (VIP) to all hosts, allowing clients to connect via this logical address while each node retains dedicated IPs for management.[62] It distributes TCP/IP traffic using algorithms like round-robin, supporting up to 32 nodes without requiring application changes or additional hardware.[62] Configuration is managed through the NLB Manager GUI or PowerShell cmdlets, where clusters are created by adding hosts, setting the VIP, and choosing unicast or multicast modes for traffic handling.[62] Upon host failure, NLB detects the issue within 10 seconds and redistributes the load to remaining nodes, enhancing availability for applications like web or VPN servers.[62]
Open-source tools like HAProxy enable software load balancing with VIPs configured at the frontend to handle incoming traffic.[63] HAProxy acts as a reverse proxy, binding frontends to a VIP (e.g., frontend http-in bind 192.168.1.10:80) to listen for connections on specified ports and IP addresses, supporting both IPv4 and IPv6.[63] Backends define server pools (e.g., backend web_servers balance roundrobin server srv1 192.168.1.11:80 check), where health checks monitor server availability via HTTP, TCP, or other probes, dynamically removing unhealthy servers from rotation.[63] Rules in the frontend (e.g., use_backend web_servers if { path /dynamic }) route traffic to appropriate backends, with a default backend for unmatched requests.[63] This setup provides high availability by allowing multiple HAProxy instances to share VIPs through external protocols like VRRP, ensuring failover without service interruption.[63]
Custom scripting in Bash or Python allows for dynamic VIP assignment based on health checks, often complementing daemons like Keepalived. In Bash, scripts utilize the ip command from iproute2 to add or remove VIPs on interfaces (e.g., ip addr add 192.168.1.100/24 dev eth0 to assign, ip addr del 192.168.1.100/24 dev eth0 to remove), triggered by periodic health checks such as ping for reachability or curl for service status. These scripts run via cron or as daemons, evaluating conditions like CPU load or service responsiveness before reassigning the VIP to a healthier node, providing a lightweight alternative for simple failover scenarios. Python scripts achieve similar functionality using the subprocess module to execute ip commands (e.g., subprocess.run(['ip', 'addr', 'add', '192.168.1.100/24', 'dev', 'eth0'])), integrating health checks with libraries like requests for HTTP probes or ping3 for ICMP.[64] Such scripts enable programmatic control, logging events and notifying administrators during VIP migrations, though they require careful error handling to avoid conflicts in multi-node setups.[64]