]> Nokia Bell Labs

sabine.randriamasy@nokia-bell-labs.com

Telefonica

luismiguel.contrerasmurillo@telefonica.com

Qualcomm Europe, Inc.

jros@qti.qualcomm.com

Deutsche Telekom

Roland.Schott@telekom.de

next generation unicorn sparkling distributed ledger Service providers are starting to deploy computing capabilities across the network for hosting applications such as distributed AI workloads, AR/VR, vehicle networks, and IoT, among others. In this network-compute environment, knowing information about the availability and state of the underlying communication and compute resources is necessary to determine both the proper deployment location of the applications and the most suitable servers on which to run them. Further, this information is used by numerous use cases with different interpretations. This document proposes an initial approach towards a common exposure scheme for metrics reflecting compute and communication capabilities. About This Document The latest revision of this draft can be found at . Status information for this document may be found at . Source for this draft and an issue tracker can be found at .

Introduction Operators are starting to deploy distributed computing environments in different parts of the network that must support a variety of applications with different performance needs such as latency, bandwidth, compute power, storage, energy, etc. This translates in the emergence of distributed compute resources (both in the cloud and at the edge) with a variety of sizes (e.g., large, medium, small) characterized by distinct dimensions of CPUs, memory, and storage capabilities, as well as bandwidth capacity for forwarding the traffic generated in and out of the corresponding compute resource. The proliferation of the edge computing paradigm further increases the potential footprint and heterogeneity of the environments where a function or application can be deployed, resulting in different unitary cost per CPU, memory, and storage. This increases the complexity of deciding the location where a given function or application should be best deployed or executed. On the one hand, this decision should be jointly influenced by the available resources in a given computing environment and, on the other, by the capabilities of the network path connecting the traffic source with the destination. Network and compute-aware application placement and service selection has become of utmost importance in the last decade. The availability of such information is taken for granted by the numerous service providers and bodies that are specifying them. However, distributed computational resources often run different implementations with different understandings and representations of compute capabilities, which poses a challenge to the application placement and service selection problems. While standardization efforts on network capabilities representation and exposure are well advanced, similar efforts on compute capabilitites are in their infancy. This document proposes an initial approach towards a common understanding and exposure scheme for metrics reflecting compute capabilities. It aims at leveraging existing work in the IETF on compute metrics definitions to build synergies. It also aims at reaching out to working or research groups in the IETF that would consume such information and have particular requirements.

Conventions and Definitions The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 when, and only when, they appear in all capitals, as shown here.

Problem Space and Needs Visibility and exposure of both (1) network and (2) compute resources to the application is critical to enable a proper functioning of the new class of services arising at the edge (e.g., distributed AI, driverless vehicles, AR/VR, etc.). To understand the problem space and the capabilities that are lacking in today's protocol interfaces needed to enable these new services, we focus on the life cycle of a service. At the edge, compute nodes are deployed near communication nodes (e.g., co-located in a 5G base station) to provide computing services that are close to users with the goal to (1) reduce latency, (2) increase communication bandwidth, (3) increase reliability, (4) enable privacy nd security, (5) enable personalization, and (6) reduce cloud costs and energy consumption. Services are deployed on the communication and compute infrastructure through a two-phase life cycle that involves first a service deployment stage and then a service selection stage ().

Service life cycle. Service +------> Service | | Service | | Deployment | | Selection | | | | | | | +-------------+ +--------------+ +-------------+ ]]>

Service deployment. This phase is carried out by the service provider and involves the deployment of a new service (e.g., a distributed AI training/inference, an XR/AR service, etc.) on the communication and compute infrastructure. The service provider needs to properly size the amount of communication and compute resources assigned to this new service to meet the expected user demand. The decision on where the service is deployed and how many resources are requested from the infrastructure depends on the levels of Quality of Experience (QoE) that the provider wants to guarantee to the users of the service. To make a proper deployment decision, the provider must have visibility on the resources available within the infrastructure, including communication (e.g., link bandwidth and latency) and compute (e.g., CPU, GPU, memory and storage capacity) resources. For instance, to run a Large Language Model (LLM) with 175 billion parameters, a total aggregated memory of 350GB and 5 GPUs may be needed . The service provider needs an interface to query the infrastructure, extract the available compute and communication resources, and decide which subset of resources are needed to run the service. Service selection. This phase is initiated by the user, through a client application that connects to the deployed service. There are two main decisions that must be performed in the service selection stage: compute node selection and path selection. In the compute node selection step, as the service is generally replicated in N locations (e.g., by leveraging a microservice architecture), the application must decide which of the service replicas it connects to. Similar to the service deployment stage, this decision requires knowledge about communication and compute resources available in each replica. On the other hand, in the path selection decision, the application must decide which path it chooses to connect to the service. This decision depends on the communication properties (e.g., bandwidth and latency) of the available paths. Similar to the service deployment case, the service provider needs an interface to query the infrastructure and extract the available compute and communication resources, with the goal to make informed node and path selection decisions. It is also important to note that, ideally, the node and path selection decisions should be jointly optimized, since in general the best end-to-end performance is achieved by jointly taking into account both decisions. In some cases, however, such decisions may be owned by different players. For instance, in some network environments, the path selection may be decided by the network operator, wheres the compute node selection may be decided by the application. Even in these cases, it is crucial to have a proper interface (for both the network operator and the service provider) to query the available compute and communication resources from the system. summarizes the problem space, the information that needs to be exposed, and the stakeholders that need this information. Problem space, needs, and stakeholders.

Action to take	Information needed	Who needs it
Service placement	Compute and communication	Service provider
Service selection/node selection	Compute and communication	Network/service provider and/or application
Service selection/path selection	Communication	Network/service and/or application

Use Cases

Distributed AI Workloads Generative AI is a technological feat that opens up many applications such as holding conversations, generating art, developing a research paper, or writing software, among many others. Yet this innovation comes with a high cost in terms of processing and power consumption. While data centers are already running at capacity, it is projected that transitioning current search engine queries to leverage generative AI will increase costs by 10 times compared to traditional search methods . As (1) computing nodes (CPUs, GPUs, and NPUs) are deployed to build the edge cloud leveraging technologies like 5G and (2) with billions of mobile user devices globally providing a large untapped computational platform, shifting part of the processing from the cloud to the edge becomes a viable and necessary step towards enabling the AI-transition. There are at least four drivers supporting this trend:

• Computational and energy savings: Due to savings from not needing large-scale cooling systems and the high performance-per-watt efficiency of the edge devices, some workloads can run at the edge at a lower computational and energy cost , especially when considering not only processing but also data transport.
• Latency: For applications such as driverless vehicles which require real-time inference at very low latency, running at the edge is necessary.
• Reliability and performance: Peaks in cloud demand for generative AI queries can create large queues and latency, and in some cases even lead to denial of service. Further, limited or no connectivity generally requires running the workloads at the edge.
• Privacy, security, and personalization: A "private mode" allows users to strictly utilize on-device (or near-the-device) AI to enter sensitive prompts to chatbots, such as health questions or confidential ideas.

These drivers lead to a distributed computational model that is hybrid: Some AI workloads will fully run in the cloud, some will fully run in the edge, and some will run both in the edge and in the cloud. Being able to efficiently run these workloads in this hybrid, distributed, cloud-edge environment is necessary given the aforementioned massive energy and computational costs. To make optimized service and workload placement decisions, information about both the compute and communication resources available in the network is necessary too. Consider as an example a large language model (LLM) used to generate text and hold intelligent conversations. LLMs produce a single token per inference, where a token is a set of characters forming words or fractions of words. Pipelining and parallelization techniques are used to optimize inference, but this means that a model like GPT-3 could potentially go through all 175 billion parameters that are part of it to generate a single word. To efficiently run these computational-intensive workloads, it is necessary to know the availability of compute resources in the distributed system. Suppose that a user is driving a car while conversing with an AI model. The model can run inference on a variety of compute nodes, ordered from lower to higher compute power as follows: (1) the user's phone, (2) the computer in the car, (3) the 5G edge cloud, and (4) the datacenter cloud. Correspondingly, the system can deploy four different models with different levels of accuracy and compute requirements. The simplest model with the least parameters can run in the phone, requiring less compute power but yielding lower accuracy. Three other models ordered in increasing value of accuracy and computational complexity can run in the car, the edge, and the cloud. The application can identify the right trade-off between accuracy and computational cost, combined with metrics of communication bandwidth and latency, to make the right decision on which of the four models to use for every inference request. Note that this is similar to the resolution/bandwidth trade-off commonly found in the image encoding problem, where an image can be encoded and transmitted at different levels of resolution depending on the available bandwidth in the communication channel. In the case of AI inference, however, not only bandwidth is a scarce resource, but also compute.

Open Abstraction for Edge Computing Modern applications such as AR/VR, V2X, or IoT, require bringing compute closer to the edge in order to meet strict bandwidth, latency, and jitter requirements. While this deployment process resembles the path taken by the main cloud providers (notably, AWS, Facebook, Google and Microsoft) to deploy their large-scale datacenters, the edge presents a key difference: datacenter clouds (both in terms of their infrastructure and the applications run by them) are owned and managed by a single organization, whereas edge clouds involve a complex ecosystem of operators, vendors, and application providers, all striving to provide a quality end-to-end solution to the user. This implies that, while the traditional cloud has been implemented for the most part by using vertically optimized and closed architectures, the edge will necessarily need to rely on a complete ecosystem of carefully designed open standards to enable horizontal interoperability across all the involved parties. As an example, consider a user of an XR application who arrives at his/her home by car. The application runs by leveraging compute capabilities from both the car and the public 5G edge cloud. As the user parks the car, 5G coverage may diminish (due to building interference) making the home local Wi-Fi connectivity a better choice. Further, instead of relying on computational resources from the car and the 5G edge cloud, latency can be reduced by leveraging computing devices (PCs, laptops, tablets) available from the home edge cloud. The application's decision to switch from one domain to another, however, demands knowledge about the compute and communication resources available both in the 5G and the Wi-Fi domains, therefore requiring interoperability across multiple industry standards (for instance, IETF and 3GPP on the public side, and IETF and LF Edge on the private home side).

Optimized Placement of Microservice Components Current applications are transitioning from a monolithic service architecture towards the composition of microservice components, following cloud-native trends. The set of microservices can have associated Service Level Objectives (SLOs) that impose constraints not only in terms of the required computational resources dependent on the compute facilities available, but also in terms of performance indicators such as latency, bandwidth, etc, which impose restrictions in the networking capabilities connecting the computing facilities. Even more complex constraints, such as affinity among certain microservices components could require complex calculations for selecting the most appropriate compute nodes taken into consideration both network and compute information.

Production and Consumption Scenarios of Compute-related Information It is important to understand the scenarios of production and consumption of compute-related information in combination with information related to communication. Leveraging such combination enables the possibility of resource and workload placement optimization, leading to both operational cost reductions to the operator and service provider, as well as an improvement on the service level experienced by the end users.

Producers of Compute-Related Information The information relative to compute (i.e., processing capabilities, memory, and storage capacity) can be structured in two ways. On one hand, the information corresponding to the raw compute resources; on the other hand, the information of resources allocated or utilized by a specific application or service function. The former is typically provided by the management systems enabling the virtualization of the physical resources for a later assignment to the processes running on top. Cloud Managers or Virtual Infrastructure Managers are the entities that manage those resources. These management systems offer APIs to access the available resources in the computing facility. Thus, it can be expected that these APIs can be used for the consumption of such information. Once the raw resources are retrieved from the various compute facilities, it could be possible to generate topological network views of them, as being proposed in . Regarding the resources allocated or utilized by a specific application or service function, two situations apply: (1) The total allocation and (2) the allocation per service or application. In the first case, the information can be supplied by the virtualization management systems described before. For the specific per-service allocation, it can be expected that the specific management systems of the service or application is capable to provide the resources being used at run time typically as part of the allocated ones. In this last scenario, it is also reasonable to expect the availability of APIs offering this information, even though they can be specific to the service or application.

Consumers of Compute-Related Information The consumption of compute-related information is relative to the different phases of the service lifecycle. This means that this information can be consumed in different points of time and for different purposes. The expected consumers can be both external or internal to the network. As external consumers it is possible to consider external application management systems requiring resource availability information for service function placement decision, workload migration in the case of consuming raw resources, or requiring information on the usage of resources for service assurance or service scaling, among others. As internal consumers, it is possible to consider network management entities requiring information on the level of resource utilization for traffic steering (as the Path Selector in ), load balance, or analytics, among others.

Metrics Selection and Exposure Regarding metrics exposure one can distinguish the topics of (1) how the metrics are exposed and (2) which kind of metrics need to be exposed. The infrastructure resources can be divided into network and compute related resources. Network based resources can roughly be subdivided according to the network structure into edge, backbone, and cloud resources. This section intends to give a brief outlook regarding these resources for stimulating additional discussion with related work going on in other IETF working groups or standardization bodies.

Edge Resources Edge resources are referring to latency, bandwidth, compute latency or traffic breakout.

Network Resources Network resources relate to the traditional network infrastructure. The next table provides an overview of some of the commonly used metrics. Examples of network resource metrics.

Kind of Resource
QoS
Latency
Bandwidth
RTT
Packet Loss
Jitter

Cloud Resources The next table provides an example of parameters that could be exposed: Examples of cloud resource parameters.

CPU	Compute	Available cpu resources
Memory	Compute	Available memory
Storage	Storage	Available storage
Configmaps	Object	Configuration and topology maps
Secrets	Object	Possible secrets
Pods	Object	Possible pods
Jobs	Object	Concurrent jobs
Services	Object	Concurrent services

Considerations about Metrics The metrics considered in this document should be used to support decisions for selection and deployment of services and applications. Further iterations of this document may consider additional life cycle operations such as assurance and relevant metrics. The network netrics listed above are specified in a number of IETF documents such as RFC 9439 , which itself leverages on RFC 7679. The work on compute metrics at the IETF, on the other hand, is in its first stages and merely relates to low-level infrastructure metrics such as in . However:

• decisions for service deployment and selection also involve decisions that require an aggregated view for instance at the service level,
• deciding entities may only have partial access to the compute information and actually do not need to have all the details.

A number of public tools and methods to test compute facility performances are made available by cloud service providers or service management businesses, see and to name a few. However, for the proposed performance metrics, their definition and acquisition method may differ from one provider to the other, making it thus challenging to compare performances across different providers. The latter aspect is particularly problematic for applications running at the edge where a complex ecosystem of operators, vendors, and application providers is involved and calls for a common standardized definition.

Metric Dimensions Upon exploring existing work, this draft proposes to consider a number of dimensions before identifying the compute metrics needed to take a service operation decision. This list is initial and is to be updated upon further discussion. Dimensions helping to identify needed compute metrics: Dimensions to consider when idenfitying compute metrics.

Dimension	Definition	Examples
Decision	what are the metrics used for	monitoring, benchmarking, service selection and placement
Driving KPI	what is assessed with the metrics	speed, scalability, cost, stability
Decision scope	different granularities	infrastructure node/cluster, compute service, end-to-end application
Receiving entity	receiving metrics	router, centralized controller, application management
Deciding entity	computing decisions	router, centralized controller, application management

When metrics are documented according to their life cycle action, it allows for a more reliable interpretation and informed utilization of the metrics. The table below provides some examples: Metrics documented by life cycle action.

Lifecycle action	Example
Acquisition method	telemetry, estimation
Value processing	aggregation, abstraction
Exposure	in-path distribution, off-path distribution

Abstraction Level and Information Access One important aspect to consider is that receiving entities that need to consume metrics to take selection or placement decisions do not always have access to computing information. In particular, several scenarios to be completed upon further discussions, may need to be considered among which:

• the consumer is an ISP that does not own the compute infrastructure or has no access to full information. In this case the compute metrics will likely be estimated
• the consumer is an application that has no direct access to full information while the ISP has access to both network and compute information. However the ISP is willing to provide guidance to the application with abstract information.
• the consumer has access to full network and compute information and wants to use it for fine-grained decision making e.g. at the node/cluster level
• the consumer has access to full information but essentially needs guidance with abstracted information.
• the consumer has access to information that is abstracted or detailed depending on the metrics.

These scenarios further drive the selection of metrics upon the above mentioned dimensions.

Distribution and Exposure Mechanisms

Metric Distribution Computing-Aware Traffic Steering (CATS) Other existing work at the IETF CATS WG has explored the collection and distribution of computing metrics in . They consider three deployment models in their deployment considerations:

• distributed among network devices directly,
• collected by a centralized control plane,
• hybrid where a part of computing metrics are distributed among involved network devices, and others may be collected by a centralized control plane.

In the hybrid mode, the draft suggests that some static information (e.g., capabilities information) can be distributed among network devices since they are quite stable. Frequent changing information (e.g., resource utilization) can be collected by a centralized control plane to avoid frequent flooding in the distributed control plane. Besides the required extensions to the routing protocols, the hybrid mode stresses the impact of the dynamicity of the distributed metrics and the need to carefully sort out the metric exposure mode w.r.t. their dynamicity.

Metric Exposure with Extensions of ALTO The ALTO protocol has been difined to expose an abstracted network topology and related path costs in . Its extension RFC 9240 allows to define entities on which properties can be defined, while introduces a proposed entity property that allows to consider an entity as both a network element with network related costs and properties and a element of a data center with compute related properties. Such an exposure mechanism is particularly useful for decision making entities which are centralized and located off the network paths.

Exposure of Abstracted Generic Metrics In some cases, whether due to unavailable information details or for the sake of simplicity, a consumer may need reliable but simple guidance to select a service. To this end, abstracted generic metrics may be useful. One can consider a generic metric that can be named “computingcost” and is applied to a contact point to one or more edge servers such as a load balancer, for short an edge server, to reflect the network operator policy and preferences. The metric “computingcost” results from an abstraction method that is hidden from users, similarly to the metric “routingcost” defined in . For instance, “computingcost” may be higher for an edge server located far away, or in disliked geographical areas, or owned by a provider who does not share information with the Internet Service Provider (ISP) or with which ISP has a poorer commercial agreement. “computingcost” may also reflect environmental preferences in terms, for instance, of energy source, average consumption vs. local climate, location adequacy vs. climate. One may also consider a generic metric named “computingperf”, applied to an edge server, that reflects its performances, based on measurements or estimations by the ISP or combination thereof. An edge server with a higher “computingperf” value will be preferred. “computingperf” can be based on a vector of one or more metrics reflecting, for instance, responsiveness, reliability of cloud services based on metrics such as latency, packet loss, jitter, time to first and/or last byte, or a single value reflecting a global performance score.

Related Work Some existing work has explored compute-related metrics. They can be categorized as follows:

• References providing raw compute infrastructure metrics: includes references to cloud management solutions (i.e., OpenStack, Kubernetes, etc) which administer the virtualization infrastructure, providing information about raw compute infrastructure metrics. Furthermore, describes processor, memory and network interface usage metrics.
• References providing compute virtualization metrics: provides several metrics as part of the Management Information Base (MIB) definition for managing virtual machines controlled by a hypervisor. The objects there defined make reference to the resources consumed by a particluar virtual machine serving as host for services or applications. Moreover, provides metrics associated to virtualized network functions.
• References providing service metrics including compute-related information: proposes metrics associated to services running in compute infrastructures. Some of these metrics do not depend on the infrastructure behavior itself but from where such compute infrastructure is topologically located.
• Other existing work at the IETF CATS WG has explored the collection and distribution of computing metrics in . In their deployment considerations, they consider three models: distributed, centralized and hybrid.

Guiding Principles The driving principles for designing an interface to jointly extract network and compute information are as follows: P1. Leverage metrics across working groups to avoid reinventing the wheel. For instance:

• RFC 9439 leverages IPPM metrics from RFC 7679.
• Section 5.2 of considers delay as a good metric, since it is easy to use in both compute and communication domains. RFC 9439 also defines delay as part of the performance metrics.
• Section 6 of proposes to represent the network structure as graphs, which is similar to the ALTO map services in .

P2. Aim for simplicity, while ensuring the combined efforts don’t leave technical gaps in supporting the full life cycle of service deployment and selection. For instance, the CATS working group is covering path selection from a network standpoint, while ALTO (e.g., ) covers exposing of network information to the service provider and the client application. However, there is currently no effort being pursued to expose compute information to the service provider and the client application for service placement or selection.

GAP Analysis From this related work it is evident that compute-related metrics can serve several purposes, ranging from service instance instantiation to service instance behavior, and then to service instance selection. Some of the metrics could refer to the same object (e.g., CPU) but with a particular usage and scope. In contrast, the network metrics are more uniform and straightforward. It is then necessary to consistently define a set of metrics that could assist to the operation in the different concerns identified so far, so that networks and systems could have a common understanding of the perceived compute performance. When combined with network metrics, the combined network plus compute performance behavior will assist informed decisions particular to each of the operational concerns related to the different parts of a service life cycle.

Security Considerations TODO Security

IANA Considerations This document has no IANA actions.

References Normative References Applications using the Internet already have access to some topology information of Internet Service Provider (ISP) networks. For example, views to Internet routing tables at Looking Glass servers are available and can be practically downloaded to many network application clients. What is missing is knowledge of the underlying network topologies from the point of view of ISPs. In other words, what an ISP prefers in terms of traffic optimization -- and a way to distribute it. The Application-Layer Traffic Optimization (ALTO) services defined in this document provide network information (e.g., basic network location structure and preferences of network paths) with the goal of modifying network resource consumption patterns while maintaining or improving application performance. The basic information of ALTO is based on abstract maps of a network. These maps provide a simplified view, yet enough information about a network for applications to effectively utilize them. Additional services are built on top of the maps. This document describes a protocol implementing the ALTO services. Although the ALTO services would primarily be provided by ISPs, other entities, such as content service providers, could also provide ALTO services. Applications that could use the ALTO services are those that have a choice to which end points to connect. Examples of such applications are peer-to-peer (P2P) and content delivery networks. Huawei Yale University Samsung Huawei Nokia Bell Labs Telefonica The cost metric is a basic concept in Application-Layer Traffic Optimization (ALTO), and different applications may use different types of cost metrics. Since the ALTO base protocol (RFC 7285) defines only a single cost metric (namely, the generic "routingcost" metric), if an application wants to issue a cost map or an endpoint cost request in order to identify a resource provider that offers better performance metrics (e.g., lower delay or loss rate), the base protocol does not define the cost metric to be used. This document addresses this issue by extending the specification to provide a variety of network performance metrics, including network delay, delay variation (a.k.a. jitter), packet loss rate, hop count, and bandwidth. There are multiple sources (e.g., estimations based on measurements or a Service Level Agreement) available for deriving a performance metric. This document introduces an additional "cost-context" field to the ALTO "cost-type" field to convey the source of a performance metric. China Mobile China Mobile Huawei Technologies ZTE New H3C Technologies This document describes the considerations and the potential architecture of the computing information that needs to be notified into the network in Computing-Aware Traffic Steering (CATS). Huawei Technologies China Mobile Orange Telefonica Juniper Networks, Inc. This document describes a framework for Computing-Aware Traffic Steering (CATS). Particularly, the document identifies a set of CATS components, describes their interactions, and exemplifies the workflow of the control and data planes. In many standards track documents several words are used to signify the requirements in the specification. These words are often capitalized. This document defines these words as they should be interpreted in IETF documents. This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion and suggestions for improvements. RFC 2119 specifies common key words that may be used in protocol specifications. This document aims to reduce the ambiguity by clarifying that only UPPERCASE usage of the key words have the defined special meanings. Informative References n.d. n.d. Samsung Electronics Alef Edge Telefonica This document proposes the extension of the TE topology model for including information related to data center resource capabilities. This document defines a portion of the Management Information Base (MIB) for use with network management protocols in the Internet community. In particular, this specifies objects for managing virtual machines controlled by a hypervisor (a.k.a. virtual machine monitor). Telefonica Nokia Bell Labs Qualcomm Europe Benocs Unicamp Service providers are starting to deploy computing capabilities across the network for hosting applications such as AR/VR, vehicle networks, IoT, and AI training, among others. In these distributed computing environments, knowledge about computing and communication resources is necessary to determine the proper deployment location of each application. This document proposes an initial approach towards the use of ALTO to expose such information to the applications and assist the selection of their deployment locations. Futurewei Microsoft Huawei Huawei Futurewei This draft describes the 5G Edge computing use cases for CATS and how BGP can be used to propagate additional IP layer detectable information about the 5G edge data centers so that the ingress routers in the 5G Local Data Network can make path selections based on not only the routing distance but also the IP Layer relevant metrics of the destinations. The goal is to improve latency and performance for 5G Edge Computing (EC) services even when the detailed servers running status are unavailable.

Acknowledgments TODO acknowledge.