| Internet-Draft | Use cases-Standalone Service ID | July 2024 |
| Huang, et al. | Expires 2 January 2025 | [Page] |
More and more emerging applications have raised the demand for establishing networking connections anywhere and anytime, alongside the availability of highly distributive any-cloud services. Such a demand motivates the need to efficiently interconnect heterogeneous entities, e.g., different domains of network and cloud owned by different providers to reduce cost, e.g., overheads and end-to-end latency, while ensuring the overall performance satisfies the requirements of the applications. Considering that different network domains and cloud providers may adopt different types of technologies, the key to interconnection and efficient coordination is to employ a unified interface that can be understood by heterogeneous parties, which could derive the consistent requirements of the same service and treat the service traffic appropriately by their proprietary policies and technologies.¶
This document provides use cases and problem statements from two main Internet traffic categories: one is the traditional north-south traffic which is defined from clients to entities (such as servers or DCs), and the other is east-west traffic, which refers to traffic between entities (such as inter-server or inter-service).Furthermore,the requirements for a standalone Service ID are also detailed in this document.¶
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The Internet application paradigm has been witnessing fundamental changes and will profoundly impact on the two most basic Internet aspects: traffic engineering and traffic steering.¶
Firstly, due to the fast and deep digital transformation across almost all sectors of industry and society, more and more applications are rapidly shifting from simply retrieving well-processed content from central servers and data centers (i.e., C/S model), into delivering multi-type computing tasks to/from cloud infrastructures, such as 3D virtual reality, picture recognition, autonomous driving and AI-model training, etc. The majority type of traffic on the Internet has, therefore, been transformed from the single best-effort flow to the multi-tasking flows with diversified and stringent performance requirements, for example, time-critical tasks demanding a deterministic end-to-end delay, large user-generated raw data requiring steady high transfer rate, and compute-intensive tasks calling for scheduled CPU cycles or destined to heterogeneous type of processors (e.g., CPU or GPU), etc. So, this will inevitably bring challenges to the methodologies and processes of current Internet traffic engineering, in which the traffic classification is insufficient to identify and guarantee SLAs of multi-tasking flows, and the network scheduling is not adaptive to the transient life cycle of computing tasks.¶
Secondly, the whole cloud computing ecosystem rapidly evolves to the cloud native paradigm. Compared to the traditional monolithic designing patterns, cloud-native applications are essentially designed and developed as distributed and connected micro-services, with each performing an independent functionality. Because each micro-service encloses all its required computing resources and logic codes in a lightweight container, it is very natural and efficient to deploy and manage replicas of services in a highly distributive and scalable way via the network. Given the stringent performance requirements, critical computing tasks should be offloaded to the maximum proximity of user-generated data for the fastest responsiveness and real-time processing. So, cloud resources residing in the central cloud, edge cloud, and communication nodes, such as base stations, vehicles, or even handheld devices, from different cloud service providers (CSPs), could be considered as ubiquitous cloud infrastructure to host service instances through the Internet. This will put great challenges on the protocols and mechanisms of Internet traffic engineering, in which the computing tasks and life cycle should be considered. As for the Internet traffic steering, in which the current addressing mechanism is inherently designed in terms of the host as well as the specific resources, however, the aforementioned service and its connections would be independent of both the specific host and resources. The same service could be deployed at multiple hosts on multiple sites upon different cloud resources, the service is actually rendered to be a standalone entity accessed and connected by its counterpart.¶
Considering the heterogeneous resources and technologies of different entities i.e., network domains and cloud providers, use cases and problem statements are presented from two main Internet traffic categories. One is the traditional north-south traffic which is defined from clients to entities (such as servers or DCs). The other is east-west traffic which refers to traffic between entities (such as inter-server or inter-service). Usually, in most edge computing scenarios, resources are insufficient and heterogeneous due to cost and energy limitations. So, instead of deploying the application with its full functionalities, the service instance has smaller resource consumptions and a shorter lifetime that fits well for these scenarios. Moreover, as for the frequent mobility of clients and fast service migration, the east-west traffic between edge cloud and central cloud, and among edge sites (such as inter-service communications), will significantly increase and greatly impact the SLA experienced by clients from the point view of application as a whole.¶
It is noticed that many technologies have been proposed in the community for appropriately handling north-south traffic and the examples are CATS and APN which have proposed frameworks and the associated service identification mechanisms in the defined scenarios. As far as east-west traffic among multiple network or cloud domains is concerned, it is generally sent through tunnels using existing approaches such as network service mesh, and as is explained in the following sections, such approaches cause large end-to-end delay and high complexity especially when multi-hop inter-service communications are involved.¶
There are complicated barriers between network and cloud entities regarding service connections or no interface between the sensitive networking service and the underlying network for either north-south traffic or east-west traffic. Therefore, employing a unified interface and entity that could be accessed by multiple network or cloud platforms is critical. Leveraging this unified entity which is temporarily called service ID, addressing and networking among heterogeneous network domains and cloud providers with consistent semantics and service SLA guarantees could be accomplished by establishing the mapping between the unified service ID and the specific technologies used by a network domain or a cloud provider.¶
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 [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here.¶
Service ID: Service Identifier.¶
OAM: Operation Administration and Maintenance.¶
CSP: Cloud Service Provider.¶
Multi-cloud [ITU-T Y. 3537]: Use of cloud services in the public cloud from two or more independent cloud service providers (CSPs) simultaneously for business.¶
SLA: Service Level Agreement.¶
APM: Application Performance Management.¶
RED: Request, Error, and Delay.¶
eBPF: enhanced Berkeley Packet Filter.¶
In the following section, three typical use case scenarios, i.e., network resources provisioning, fine-grained traffic steering among multiple service instances, and observability of end-to-end services, are described for conventional north-south traffic circumstances. A problem description and gap analysis, with requirements, will be provided.¶
The Internet has long been used as a pipe to deliver the north-south traffic from a client to a server. However, with the stringent requirements raised by newly emerging applications such as Augmented Reality and Virtual Reality and AI-based services, the requirements of introducing the application-related information into the network and providing differentiated and fine-granular treatment for a various distinctive applications and services which require network capabilities exceeding Best Effort are increasing. To this end, application-aware networking (APN) has been proposed to solve the problem in [I-D.li-rtgwg-apn-app-side-framework]. Nevertheless, fine-grained awareness could be extended into sub-service of application for which the conventional 5-tuples would be hard to identify.¶
The current Internet adopts a fixed IP address interconnection mode, and when a service is invoked, it is generally required to first query the IP address corresponding to the service name through DNS. Within a possible ubiquitous distributed service scenario, the efficiency of querying IP addresses through DNS would be relatively low for often requiring multiple redirects to find the most appropriate service instance, which cannot meet the fast response needs of high interaction applications such as AR/VR and autonomous driving. In addition, when the client moves or the server migrates, the traffic flow will initiate a new handshake process, which cannot meet the performance requirements of access agility and being always online.¶
Also, it is well acknowledged that for some distributed services, the performance experienced by clients depends not only on network metrics such as bandwidth and latency but also on cloud metrics such as processing, storage capabilities, and capacity. Computing aware traffic steering (CATS) working group is working on this. For cases mentioned in [I-D.ietf-cats-usecases-requirements], Cloud VR/AR, for instance, brings challenging requirements to both network and computing. Correspondingly, CATS enables distributed edge nodes to serve a service request with carefully selected instances which guarantees it has sufficient computing resources and ensures that the network path meets end-to-end delay requirements by introducing computing metrics into the conventional routing scheme. Other use case scenarios included in [I-D.ietf-cats-usecases-requirements] involve computing-aware intelligent transportation, digital twin, SD-WAN, etc. CATS will also provide agile service access and enhance the utilization of network and computing resources.¶
Compared to IP-based addressing and routing schemes, service-based interconnection and routing would align more with the essential demands and expectations of clients and services. Thus, it would be instructive to identify and indicate services in the interconnected network to steer and guarantee north-south traffic.¶
To locate performance bottlenecks, prevent failures, and improve resource utilization efficiency, many technologies have been developed for measuring the traffic and monitoring the network status. Examples of these technologies include bidirectional forwarding detection (BFD), in-band network telemetry (INT), and packet loss and delay management for MPLS. However, the primary goal of such technologies is facilitating network operators to conduct operations, administrations, and maintenance (OAM), so these technologies generally collect statistics associated with a link or a path in a network domain, but fail to provide measurements of an end-to-end connection from a client to a server. In fact, due to a lack of service semantics, extensive efforts are required to correlate the statistics of observed metrics with specific applications and services. Furthermore, relevant schemes, e.g., ping and keepalive, do exist and provide the client-to-server end-to-end detection, while such schemes generally work at the application level and fail to provide information and guidance for lower layers, e.g., L3 and L4. Consequently,achieving whole-stack observability for the north-south traffic of end-to-end services remains a problem.¶
In the following, three typical use cases, i.e., connectivity, scheduling, and observability, of east-west traffic will be described, considering the evolution of architecture from one cloud to multi-cloud and even multi-CSP. The burdening complexity and the hinderances for service performance with existing methods are demonstrated for each use case.¶
In the service mesh architecture, inter-service communication is generally conducted using sidecar proxies that are collocated with service pods. A sidecar proxy intercepts all incoming traffic of the collocated service pod and conducts appropriate processing, such as service discovery, routing, or rate limiting. After receiving packets processed by the service pod, the sidecar proxy sends the packets to the next-hop sidecar proxy. The selection of the next-hop node may be subject to various criteria such as load balancing. Consequently, it is essential to consider the application semantics in the selection, which facilitates communication between adjacent sidecar proxies with layer-7 protocols such as gRPC, or REST API.¶
When the service mesh architecture extends from one cloud domain to multi-cloud domains, gateways are needed in inter-service communications. These gateways are generally connected, e.g., by tunnels, to ensure they are reachable to each other. As shown below, micro-service A is located in cloud domain A, and micro-service B is located in cloud domain B. Both cloud domains can be owned by the same CSP or even different CSPs. Cloud gateways A and B are deployed to access the micro-services in their internal domain. Consequently, the communication between micro-services A and B consists of three TCP segments, i.e., from sidecar proxy A to cloud gateway A, from sidecar proxy B to cloud gateway B, and between gateways A and B.¶
|Incoming
|traffic
+-------v--------+ +-----------------+
| cloud GW A |------------>| cloud GW B |
+----|------^----+ Tunnels etc +--------|--------+
| | |
+----v------|----+ +--------v--------+
| sidecar proxy A| | sidecar proxy B |
+----|------^----+ +--------|--------+
| | |
+----v------|----+ +--------v--------+
| microservice A | | microservice B |
+----------------+ +-----------------+
cloud domain A cloud domain B
It can be seen that each hop inter-service communication includes processing delay at the two gateways of both cloud domains for operations such as encapsulation and decapsulation, service discovery, routing, and load balancing. When the two domains adopt different technologies such as cloud topology and routing protocols, the two gateways further serve as interfaces and establish appropriate mapping between the different technologies. If an application requires multi-hop inter-service communications, e.g., switching to other CSPs for failure recovery, extending micro-services chains for performance promotion, or supporting service continuity of a moving client, the complexity of managing the application is tremendous and the end-to-end delay of the application would always exceed the maximum tolerable latency requirements.¶
Services from remote clusters should be created locally via current existing APIs, ServiceEntries for instance, in a name.namespace.global format. DNS resolution is provided by CoreDNS. With a remote service registered, the sidecar of an application pod redirects traffic to the cluster IP and steers it to the remote gateway. Remote gateways among various clusters require fundamental connectivity via LAN or WAN. As for local entities determining a preferred remote endpoint, strategies will be implemented as instructed by definitions and configurations in VirtualServices and DestinationRules.¶
(Configured in ServiceEntry)
Service B:
Cloud 1 Gateway Cloud 2
Cloud 2 Gateway +-------------+
| |
(Configured in VirtualService) | |
Match TAG I: +-------+ -- |
Cloud 1 Gateway +---->|Gateway|--->( ) |
Match TAG II: / +-------+ -- |
Cloud 2 Gateway / | Service B |
/ | |
/ +-------------+
+-------------+ / +-------------+
| | / | |
| |/ | |
| -- +-------+ +-------+ -- |
| ( )--->|Gateway|-------->|Gateway|--->( ) |
| -- +-------+ +-------+ -- |
| Service A | | Service B |
| | | |
+-------------+ +-------------+
Cloud 1 Cloud 3
In order to be aware of and access multiple distributed service instances of remote services, remote gateways need to be registered as endpoints in the local cluster. Furthermore, the steering strategy is comparatively static. It is almost impossible to always rewrite configurations in ServiceEntries, VirtualServices, and DestinationRules. Thus, it is challenging to dynamically steer the traffic among different clusters and edge clouds, aiming to select an optimal or most appropriate endpoint. Network infrastructure connects edge gateways rather than services, making it unable to be aware of the information and requirements of the services it carries. Thus, it would be non-trivial to provide corresponding fine granular services provisioning.¶
The gaps and problems are concluded as follows:¶
Maintaining and managing dynamic remote service endpoints under the service name makes real-time maintenance and dynamic management difficult within a distributed manner.¶
Service endpoints and routing strategies are unaware of remote cluster capabilities and network status, making dynamic optimization and scheduling difficult.¶
The non-invasive grayscale release of service mesh has become a mature feature. However, in the context of the widespread adoption of cloud-native applications, applications often no longer exist in the form of individual services but are decomposed into a series of cloud-native micro-services deployed in various clusters, where there are chains among services in which micro-services jointly provide services to the customers.¶
Similar to the service function chain (SFC) defined in L3, the micro-service chain (MSC) is correspondingly proposed for conditions in L7. When there is an invoking link between micro-services, the grayscale release of services is often not limited to a single micro-service but requires environmental isolation and traffic control of the entire micro-service chain.¶
+-------------+
| -- |
| ( ) |
| -- |
/| Service A |\
/ +-------------+ \
/ Cloud 1 \
| v || v |
| +-------------+ || +-------------+ |
| | -- | || | -- | |
| | ( ) | || | ( ) | |
| | -- | || | -- | |
| | Service B | || | Service B | |
| +-------------+ || +-------------+ |
| |Cloud 2 || | Cloud 4 |
| v || v |
| +-------------+ || +-------------+ |
| | -- | || | -- | |
| | ( ) | || | ( ) | |
| | -- | || | -- | |
| | Service C | || | Service C | |
| +-------------+ || +-------------+ |
| Cloud 3 || Cloud 5 |
LANE 1 LANE 2
Distinguishing and isolating applications according to versions or other features into separate operating environments is defined as traffic lanes. Then, by configuring traffic lane rules, traffic could be steered into the target lane.¶
However, gaps may exist for which traffic lanes are required to be pre-configured and established. Traffic could be steered into respective traffic lanes according to specific tag fields or features. Specific service instances would be named when a traffic lane is configured. Though a loose mode for traffic lanes may be introduced in which instances in other lanes may not be named, but rather quote corresponding ones from the main lane, it still may not implement adjustments dynamically. Furthermore, separate service endpoints and network segments are unaware of a chain scheduling logic, making it difficult to ensure cross-service consistency and provisioning capabilities.¶
Thus, it would be beneficial to examine service performance and identify the end-to-end SLA requirements for a specific service or a target micro-service chain when correspondingly steering the traffic. Dealing with the possibility of traffic congestion and overload scenarios, dynamic scheduling capabilities of the network would be correspondingly utilized.¶
Serverless is a model based on cloud computing, which is a collection of FaaS (Function as a Service) and BaaS (Backend as a Service). CSPs host computing, storage, databases, and other computing-related resources, dynamically manage and allocate them, and then provide services to clients.¶
When a service request reaches an edge cloud's GW or load balancer, a request process module queries the instance management module to determine whether there are available idle instances. When there is a sudden increase in service requests, the resource scheduling module will apply for expansion and create new instances.¶
+--------------------------------------------------+
| +---------+ +----------+ +-----------+|
| +->| Request |----->|Instance |--->|Resource ||
|/ | Process | |Management| |Secheduling||
/ +---------+ +----------+ +-----------+|
+---------------+ /| \ trigger Initiate | Create | |
| Gateway / |/ | +--------------+ | | |
| Load Balancer | | \ | | |
+---------------+ | vv | |
^ | +--------+ | |
| | |Instance|<-------+ |
| | | (new) | |
| | +--------+ |
| | |
| | +--------+ +--------+ +--------+ +--------+ |
| | |Instance| |Instance| |Instance| |Instance| |
Request | +--------+ +--------+ +--------+ +--------+ |
| |
| +--------+ +--------+ +--------+ +--------+ |
| |Instance| |Instance| |Instance| |Instance| |
| +--------+ +--------+ +--------+ +--------+ |
+--------------------------------------------------+
However, the resources of a single resource pool or edge cloud are always limited. In the context of ubiquitous resources and services, service scheduling urgently requires identifying the expectations of a service request and perceiving the distribution and utilization of resources in order to schedule requests and achieve optimal workload distribution dynamically.¶
In the current service mesh, observability is generally conducted on a one-cloud basis using application performance management (APM) approaches such as distributed tracing. However, when the service mesh architecture moves from one cloud domain to multi-cloud domains, e.g., edge clouds that are distributed in different physical locations or multiple clouds that are owned by different CSPs, existing approaches have two major shortcomings. First, APM approaches conduct instrumentation to obtain measurements such as traces, metrics, and logs, which require the modification of codes and the re-publish of applications. However, in the multi-domain scenario, such an intrusive process either is not allowed or leads to maintenance difficulties such as conflicts of codes, which hinders the adoption of the APM approaches. Second, APM approaches focus on collecting statistics associated with the business logic and the micro-service framework, but fail to obtain measurements regarding the infrastructure such as system calls and network transmissions. This feature causes observation blind spots to service mesh in the multi-cloud scenario since inter-service communication generally goes through a complicated transmission path comprising various gateways. For example, one transmission path between two micro-services A and B may go through the pod, node, KVM virtual machines, and other infrastructure such as gateways.¶
To complement APM approaches, new technologies such as the enhanced Berkeley Packet Filter (eBPF) are introduced to collect statistics associated with the cloud-native infrastructure such as system calls, various gateways, and sidecars. The statistics are then aggregated to enable the calculation of performance metrics, e.g., RED (Request/Error/Delay), for the entire stack and facilitate distributed tracing through the correlation of call logs. However, since the byte streams collected by the eBPF technologies generally do not contain business semantics, it is difficult to conduct aggregation, especially in cross-thread communication and asynchronous invocation scenarios. Moreover, since the underlay network is invisible to the tunnel if a failure is detected in the underlay network, there is no way for the eBPF approach to correlate with the overlay tunnel and take action promptly. Consequently, achieving whole-stack observability for the east-west traffic of end-to-end services remains a problem.¶
In this section, requirements of service identification for routing network have been identified based on the use cases.¶
REQ 1 Service identification SHOULD have standalone semantics against 5-tuples.¶
REQ 2 Service identification SHOULD have global and unified semantics across terminal, network, and cloud.¶
REQ 3 Service identification SHOULD be able to index the specified service profile in terms of its SLA requirements.¶
REQ 4 Service identification SHOULD be authenticatable.¶
REQ 5 Service identification MAY indicate specified networking capabilities and specified applications as well as application components such as micro-services.¶
REQ 6 Service identification MAY cover only the selected services and applications that have been designated to be either networking or computing-sensitive.¶
REQ 7 Service identification MAY be carried across layers from L7 to lower layers such as L3 and L4.¶
TBA.¶
The authors would like to thank Ge Chen, Dongyu Yuan, Huakai Fu,Yong Guo and Cheng Huang for their comments and suggestions.¶