TppFaaS: Modeling Serverless Functions Invocations via Temporal Point Processes

Code of the paper TppFaaS: Modeling Serverless Functions Invocations via Temporal Point Processes by the authors Markus Steinbach, Anshul Jindal, Mohak Chadha, Michael Gerndt, and Shajulin Benedict.

Description

We introduce our developed system called TppFaaS, for modeling function invocations in FaaS applications using temporal point processes (TPPs). It is designed for applications running on the OpenWhisk FaaS platform, that underneath uses a Kubernetes cluster. For modeling, trace data of application functions is collected and is used for training TPP models. Based on these models, predictions are carried out. Additionally, for creating the dataset for training TPP models, we created a component within TppFaaS called Sampler. The Sampler is an automated pipeline for creating simulated FaaS applications by specifying configuration parameters. Here, an application is a function composition in which sleep commands simulate the execution times of the functions following a distribution. This simulated application is deployed on the OpenWhisk FaaS platform. For generating the traces, Sampler sends user requests to the deployed application (Step 1 in the figure above) executed by OpenWhisk. The OpenTelemetry library instruments the application's functions and exports a span for each function invocation to the post-processing service Trace Collector (Step 2). The Trace Collector enriches the span with meta-information retrieved from the OpenWhisk API (Step 3) and subsequently exports it to Zipkin (Step 4). Here, the spans are aggregated into traces and then fetched by the Sampler, which transforms the traces into a data format suitable for the TPP models (Step 5). Once a trace dataset is generated, we split it into a training and test dataset. We use the training data to optimize the parameters of the TPP model (Steps 6-7), which we then evaluate using the test data (Step 8).

Prerequisite: OpenWhisk

OpenWhisk deployed on Kubernetes is a prerequisite. If it is not yet available, detailed instructions for deploying OpenWhisk on Kubernetes is provided here.

Deployment & Configuration

Set up TppFaaS by executing the following steps:

1. Deploy Zipkin in your Kubernetes cluster. A simple manifest is provided in infra/zipkinot.yaml, which defines a Zipkin instance storing all the data in-memory. To handle high workloads and guarantee persistency, a Zipkin instance using Elasticsearch as storage is recommended. How to define Zipkin using Elasticsearch is described here.
2. Configure and deploy the Trace Collector service in your Kubernetes cluster as described here.
3. If necessary, change the OpenWhisk and Trace Collector configuration parameters in apps/config.yaml. These parameters are accessed inside the serverless functions to send requests to the OpenWhisk and Trace Collector API.
4. Configure the parameters in sampler/config.yaml which are accessed by the Sampler to send requests to OpenWhisk and to fetch the traces from Zipkin.

Generating Datasets: Sampler

The Sampler is a command-line tool for generating trace datasets used to train and evaluate TPP models. It creates a dataset by sending n requests to the FaaS application's main function at irregular time intervals. The time intervals between requests are drawn from a continuous uniform distribution with an interval specified by the lower (-l) and upper bound (-u) arguments. The arguments are set by the user, who thus determines the load on OpenWisk and, indirectly, the number of cold starts. Another feature of the Sampler is performing requests in batches, pausing requesting after each batch for a user-specified duration. The batch size and the pause duration are specified with the -b and -w arguments, respectively. To simplify the trace dataset generation process, the Sampler is an end-to-end pipeline that contains all the necessary steps for data generation, such as deploying the application. The output is a dataset in /data consisting of n traces whose format is compatible with training a TPP model.

Prerequisites

• Python 3.9
• Serverless Framework 2.19.0
• Node.js

Usage

pip install --file requirements.txt

cd sampler/bin

bash sample.sh -d sequence -n 1000 -l 2.0 -u 6.0

bash sample.sh -d sequence -n 1000 -l 2.0 -u 6.0 -b 50 -w 120 -e 2 -m 3 -r

Run it as a background process and write the error & info logs to a file:

bash sample.sh -d sequence -n 1000 -l 2.0 -u 6.0 &> run.log &

• -d = directory name of the Serverless app
• -n = number of traces to sample
• -l = lower bound of inter-request duration in seconds
• -u = upper bound of inter-request duration in seconds
• -b = batch size
• -w = pause duration after each batch in seconds
• -r = randomized function duration (sleep command's duration is drawn from a gamma distribution)
• -e = number of function duration anomalies in each trace
• -m = number of missing function anomalies in each trace

Data Format

The data format is based on the format of the paper Intensity-Free Learning of Temporal Point Processes.

{
    "sequences": [
        {
            "arrival_times": [
                1620831914775,
                1620831915292,
                1620831916205,
                ...
            ],
            "marks": [
                2,
                0,
                1,
                ...
            ],
            "wait_times": [
                169,
                138,
                4319,
                ...
            ],
            "init_times": [
                141,
                197,
                186,
                ...
            ]
        }, 
        ...
    ],
    "mapping": {
        "sequence-dev-f1": 0,
        "sequence-dev-f2": 1,
        "sequence-dev-main": 2,
        ...
    }
}

Default FaaS Applications

Multiple simulated FaaS applications are provided for data generation in /apps. All applications are implemented using the Serverless Framework. Sleep commands simulate the execution times of the FaaS functions. The command's duration is either fixed, e.g. 300 ms, or is drawn from a gamma distribution with a mean value of 300 ms at each invocation. The images below show the structure of the applications sequence ...

... and tree_large ...

... where, e.g., 300ms specifies either the sleep command's fixed duration or the mean of the gamma distribution.

Build your own FaaS Application

The template in apps/template guides the creation of custom simulated FaaS applications.

TPP Model

We used the TPP model LogNormMix from the code by Shchur, Biloš and Günnemann. After installing the dependencies with pip install --file requirements.txt, one can train and test the model interactively in models/ifltpp/interactive.ipynb. Also, setting mae_loss = True predicts the time of the next invocation as a scalar value instead of a probability distribution. In our paper, we refer to this model as TruncNorm.