AWS Machine Learning certification

The AWS Machine Learning (ML) certification is a demanding exam that requires the mastery of AWS IT infrastructure, eg., Kinesis; Statistics, eg., Principal Component Analysis (PCA); an expert level familiarity with AWS SageMaker, a one-stop shop for ML in the AWS console; and modeling with a large variety of algorithms, e.g., XGBoost, K-NN, Linear Learner, etc. In short it requires background in Machine Learning, especially in model tuning, in Statistics, and in the AWS cloud. This post is aimed at those who wishes to both learn the practice of ML in the AWS Cloud, and prepare for the AWS Speciality ML certification.

Perceptrons

I suspect that there are many Computer Scientists, IT professionals, Business leaders, and others, who are drawn to the field of ML by the ubiquity of its applications, and by the fact that the cloud opened up the practice of ML to anyone who is interested. I was first introduced to ML by Professor Jan Mycielski, at the University of Colorado at Boulder, who gave me his copy of Perceptrons by Marvin Minsky and Seymour Papert, written in 1969 with a second printing in 1972. The subtitle of Perceptrons is An Introduction to Computational Geometry, and the emphasis of this visionary book (pun intended), which laid the foundations of ML, is on what we would call today object recognition. Indeed, the book’s approach is through the problem of computer vision. Many of the mathematical ideas proposed in the book lay dormant for years, as the hardware needed to run the required computation did not exist at first, and later was the domain of a few scientists with access to mainframes. But today, thanks to the economies of scale of computing allowed by the cloud, anyone can set up a ML training job for a few hundred dollars. Of course, this led to an explosion of the field, and its great applicability in medicine, finance, weather predictions, recommender systems, etc., attracted both enthusiasts and professionals. In my academic and consulting work I have been asked to contribute to problem solving with ML, and the AWS ML Pilot which graciously invited out campus to participate, as well as a recent paper I co-authored on applications of ML to enrollment, spurred me to learn more about ML. A great place to start is the AWS ML certification, as it requires both a theoretical understanding of the field (attractive to academics) and an understanding of the ML pipeline based on AWS tools (attractive to practitioners).

ML Pipeline

A good way to study for the ML certification is to follow the ML pipeline, which consists of four main stages, which coincide with the four domains of the exam guide (Specialty MLS-C01 Exam Guide v1.2):

  1. Data Engineering (20%)
  2. Exploratory Data Analysis (24%)
  3. Modeling (36%)
  4. ML Implementation and Operations (20%)

The percentages indicate the fraction of the exam (65 questions total) dedicated to the given domain. As can be seen, Modeling, consisting of stats, algorithms, tuning and evaluation, is the largest portion. This sets apart the ML certification from other AWS certifications, as it includes a fair amount of theoretical material.

Data Engineering

This domain covers how to create data repositories, eg., a Data Lake, how to ingest data into the repository, and then how to transform the raw data in the repository into data that can be analyzed. This last step is known as a data cleaning operation.

An example of a typical solution is an S3 bucket that hosts the Data Lake, a massive dump collecting data from various sources. This data is then worked on by an Extract-Transform-Load (ETL) application hosted on an Elastic Map Reduce (EMR) cluster. The type of work done here consists in taking the data from a heterogenous set of sources (JSON files, text files, Relational Data Base dumps, images, etc.), and making the data uniform, conforming to a set of conventions described by a table of items (rows) with attributes (columns). The ETL application is typically something like Apache Spark or Apache Hadoop. The data is then written back into the S3 bucket hosting the Data Lake (or possibly a new S3 bucket). The data is now ready, and commonly living in a Pandas table, for consumption by the second stage of the pipeline: Exploratory Data Analysis.

If an exam question has qualifiers such as “set up with little effort” or “minimal management,” this may be an indication that Glue, a serverless data solution, might be preferable to setting up an EMR. This blog post describes how to create a Glue based pipeline.

Here is an interesting blog post on how to preprocess input data before making predictions using a SageMaker Inference Pipelines and Scikit-learn.

Exploratory data analysis

In this stage, data is sanitized. This can mean, for example, taking a variety of date formats (eg., January 23, 2021, 01/23/2021, 23-1-21, etc.) and making them uniform; or, dealing with missing or incomplete data.

ML takes numeric data only, and so all columns have to contain numbers. This may mean taking ordinal data (such as large, medium, small) or nominal data (such as colors), and representing it with numerical data. A subtle point here is that large, medium, small may be translated into 3,2,1, as the numbers represent the order, but the same should not be done with colors where there is no natural ordering to them. In the case of colors, we may want to use one-hot encoding: replace the column with color names with a set of columns with headings for the different colors, as in this example:

ColorRedBlueGreen
Red100
Blue010
Green001

There are two techniques for dealing with missing data:

  1. Remove rows or columns containing missing data
  2. Impute missing values, that is, interpolate the missing values by replacing them with the mean of the column, or simply zero, or a little bit more advanced, using regression, very commonly linear regression, which assumes that the data can be estimated well from a linear combination of the existing entries. We will take the opportunity here to mention an excellent source to learn ML: Dive into Deep Learning, and see the 3.1. Linear Regression.

Once the data is sanitized and resides in a table it is possible to perform feature engineering on it. Note here that there are two related terms: attributes and features. Attributes come with the raw data; they are given. Features, on the other hand, are those attributes we select to run the training process. Part of feature engineering is to select appropriate attributes for features.

For example, in detecting fraudulent credit card transactions, it may not be necessary to include the transaction id, which may be generated randomly and carry no information needed to train a model. Thus we drop the transaction id attribute, i.e., it does not become a feature. Another example may be when predicting school enrollments (which students end up coming in the fall based on their applications), it may not be necessary to have both SAT and ACT scores; the two scores may be highly correlated, in which case we only need one of them to train the model. The correlation of two attributes may be found visually with a correlation matrix or a scatter matrix.

The process of removing attributes and/or combining them is called dimensionality reduction, and there are two techniques for it:

  1. Principal Component Analysis (PCA)
  2. t-Distributed Stochastic Neighbor Embedding (t-SNE)

It may be confusing that PCA and t-SNE are ML algorithms, in fact unsupervised ML algorithms, which are also used to prepare data for ML training. There are difference between PCA and t-SNE, discussed, for example, in this StackExchange post.

Modeling

As with any advanced field in the sciences, it is good to be familiar with the nomenclature, in particular the difference – in the context of ML – between algorithm, model and framework:

  1. Algorithm: In general, algorithms are step by step instructions that turn inputs into outputs. Algorithms are a basic object of study of Computer Science, and they have been defined formally (see for example Knuth’s The Art of Computer Programming, Volume 1). In the context of ML, algorithms take as input your data and output a model. For example, in the case of the Linear Regression algorithm, the input is a set of observations, and the output is a linear function with a bias. The SageMaker algorithms, which are the algorithms needed for the exam, can be found here.
  2. Model: the interpretation of the data obtained for the sake of predictions, computed with an algorithm. The quality of a model depends on the selection of an appropriate algorithm, the fine tuning process, and the testing.
  3. Framework: it is a set of software tools, libraries and interfaces used to compute models with algorithms. For example, the textbook Dive into Deep Learning, proposes three frameworks: MXNET, PYTORCH and TENSORFLOW, all three frameworks are open source, developed by Apache, Facebook and Google, respectively. SageMaker supports all three frameworks, as well as others that can be seen here.

We should also add tensors to the list useful definitions. There seems to be confusion regarding what is a tensor. The confusion may arise from the generality of the concept; many mathematicians have learned the concept in a book such as Spivak’s Analysis on Manifolds; physicists use tensors in mechanics. For the sake of ML, the most useful way to conceptualize tensors is as a generalization of the sequence: scalar (0-dim tensor), vector (1-dim tensor), matrix (2-dim tensor), and now a “cube matrix”, indexed by (i,j,k) is a 3-dim tensor, etc. Indeed they are called ndarray in MXNet. Tensors facilitate the designation of linear transformations in n-dimensional vector spaces. See here for more.

The primary interface to SageMaker is the Jupyter Notebook, a development environment popular with Data Analysts. A Jupyter notebook has a kernel which is the computational engine on which the notebook runs, and both Python and R are natively supported on SageMaker notebooks. When opening a new Jupyter Notebook in SageMaker, the user can select a kernel which supports a given framework.

The first step in the area of Modeling is to cover the different SageMaker algorithms, all listed here. The Table: Mapping use cases to built-in algorithms in the linked document is especially useful, as it lists the algorithms according to use cases. We summarize them here:

  1. Supervised Learning:
    • Binary or Multi-class classification; eg., a spam filter
    • Regression; eg., estimating home values
    • Time Series Forecasting; eg., predict sales
      The algorithms here are DeepAR for Time Series, and for the first two, classification and regression, they are: Factorization Machines, K-NN, LL, XGBoost
  2. Unsupervised Learning:
    • Feature Engineering (PCA); eg., combine several features into one (component)
    • Anomaly Detection (RCF); eg., find outliers that make model training more difficult, since the “regular” points without outliers lends themselves to a simpler model
    • Embedding high to low dimension (Object2Vec)
    • Clustering or Grouping (K-Means); for discrete groupings within data
    • Topic Modeling (organize docs into topics not known in advanced: LDA, NTM)
  3. Textual Classification:
    • Text classification into pre-defined categories (BlazingText)
    • Translation, summary or speach2text (Seq2Seq)
  4. Image Processing:
    • Image and multi-label classification
    • Object detection and classification
    • Computer Vision, as in self-driving cars

Hyperparameters are values given to a particular ML algorithm that control its runtime: size of steps, constants, batch sizes, etc. Choosing the right hyperparameters is an art form, and it is acquired by experience, and explained to some extent here. Note that just as we used ML for dimensionality reduction, we can also use ML to tune hyperparameters – this is done with Baysian search and explained in the link just given. In order to help with the understanding of hyperparameters, I recommend reading Linear Regression Implementation from Scratch, where basic hyperparameters such as learning rate, minibatch size, epoch and gradient ascent rate are explained with great examples.

A framework has been selected, and algorithm chosen, a model constructed; how do we know the quality of the model? We need to be able to test against some data that was not used in the training, but for which we know the targets. To that end, it is customary to train the model on 80% of the data, and reserve 10% for validation, used while building the model, and 10% for testing, done at the end. Let’s concentrate on the supervise binary classification case.

Confusion Matrix

The first step of testing is to build a confusion matrix, which counts how many True Positives (TP), False Negatives (FP), False Positives (FP) and True Negatives (TN) there are. For example, TP are those items which were predicted as positive by the model, and were actually positive; FP are those items which were predicted positive erroneously by the model, since they are in fact negative. There are several metrics associated with a confusion matrix. In the diagram to the left we show Precision, which is TP/(TP+FP), and Recall, which is TP/(TP+FN). Imagine that our model is classifying MRI images according to whether cancer is present or not. It is desirable to identify all images with cancer, even at the cost of having some false positives (the argument being that a dramatic scare is preferable to a tragic neglect of treating a cancer). Thus, in this case high recall can be striven for at the cost of a moderate precision. Note that both recall and precision have a value in [0,1], and a recall close to 1 implies a FN close to zero. There are various other metrics well explained here; Wikipedia has an intro to confusion matrices (note they flipped actual and predicted classes relative to ours).

Implementation and operations

A ML model exists, and now we want to deploy it. In this domain Containers make an appearance, and some familiarity with the concept is necessary (containers are covered in detail in the AWS Developing certification). Another fundamental deployment concept is that of an endpoint. An endpoint is where we attach the model once ready to make inferences; it is a fully managed service that allows real-time inferences via a REST API (see here and here).

Deployment of a model

The components of a typical deployment, going right to left in the left figure, is an API managed by AWS API Gateway, that connects to a model endpoint, created with a single line of code in, say, a Python SDK, which then connects to a load balancer which distributes the queries to the model hosted in containers on EC2 instances, possibly spread in several Availability Zones, and part of an auto-scaling group. Note that when a SageMaker model is being trained it is housed in a container, and then the same container, but now with parameters set post-training, is used in the deployment. Also note that endpoints are flexible, in the sense that it takes relatively little effort to have more than one model behind an endpoint (using a shared serving container), with A/B testing supported. The multi-model deployment on a single endpoint, rather then several endpoints, is a good answer to a question that emphasizes low deployment cost, as it reduces deployment overhead since SageMaker manages loading models in memory and scaling them based on the traffic patterns (see here and here).

The above endpoint would work on sporadic queries, but what if the batch or streaming predictions are required? For batch predictions, raw data may be put in an S3 bucket, transformed by an ETL process (EMR + Apache Spark, or Glue), and using a batch transform ingested by the model (see here; note that one of the advantages of batch transform is that you can feed batch data to a model without deploying a persistent endpoint). For streaming predictions, data may be ingested by Kinesis, which connects with SageMaker.; see this blog post. Also see this blog post on Kinesis ingestion of video streams.

Exam Resources

  1. AWS official Machine Learning certification site
  2. AWS Ramp-Up Guide: Machine Learning
  3. AWS Certified Machine Learning – Specialty (MLS-C01) Exam Guide
  4. Exam Prep for AWS Certified Machine Learning Specialty
  5. GitHub repository with AWS SageMaker examples
  6. Great sequence of AWS YouTube videos on SageMaker
  7. The Elements of Data Science on AWS Training and Certification is very good
  8. Rules of Machine Learning: Best Practices for ML Engineering

AWS Developer certification – Associate level

The Developer certification exam is interesting, in that it covers in detail the AWS best practices for CI/CD, Continuous Integration / Continuous Delivery and Deployment, which is very nicely covered in the following white paper: Practicing Continuous Integration and Continuous Delivery on AWS, with the subtitle: Accelerating Software Delivery with DevOps. (I am referencing the June 2017 version of this white paper.) This document is well written, of especial interest to Software Engineers. While Development is the principal component of this certification (30%), there are altogether five domains:

  1. Deployment (22%)
  2. Security (26%)
  3. Development with AWS Services (30%)
  4. Refactoring (10%)
  5. Monitoring and Troubleshooting (12%)

Some of these domains overlap with other certifications. For instance, the 2nd domain, Security, is covered in detail in the Security Specialty exam, which I passed in December 2019 (and described in this post from Dec 3, 2019), and all the domains refer to the knowledge contained in the Solutions Architect certification (which I passed in the spring of 2019; see this post). However, I had to acquire a lot of new knowledge. For instance, the certification assumes advanced knowledge of some programming language, and since the Python3 SDK is one of the best developed AWS SDKs, I studied to become familiar with boto3, the AWS SDK for Python3; see here.

Of course reading manuals to understand boto3 is boring; I suggest to find a project that you always wanted to implement, and work on that. The excitement of building an application helps with the learning of a new tool. I worked, topically, on a pandemic simulator and an url shortener (which I called Tout Court) as I always wanted to have my own bit.ly application.

In order to develop both applications, I used a set of AWS tools that are covered in depth in the Deployment and Development domains: Cloud9 for writing the code (I was happy to find out that Cloud9 has a “Vi Editor” mode), I used GitHub instead of CodeCommit, but GitHub can be integrated into the AWS development environment, CodeDeploy in order to automate the deployment of the applications, and CodePipeline to bind it all together. X-Ray is an important tool for the exam, and helps to isolate “bottle-necks” in your application.

Refactoring is an interesting concept. It means to re-architect or re-imagine an existing solution but leveraging cloud-native capabilities. I learned quite a bit about it from Ahead in the Cloud: Best practices for navigating the future of enterprise IT, by Stephen Orban from AWS.

As AWS certification requires a significant investment of time (for me at least), it is important to understand why one does it. In my case, as a Computer Scientist, I believe it is important to systematically acquire new knowledge, as ours is a fast developing field. I also find the AWS curriculum very well designed, interesting, in-depth, and I have become fascinated by the new paradigm of Cloud Computing. Finally, the most important reason for me is to be able to bring this expertise back to campus, and share with students, and given them an edge in the job market upon graduation.

AWS re:Invent, Las Vegas, 2019

I am attending my first AWS re:Invent conference, Las Vegas December 2-6, 2019.

The conference is enormous, with over 60,000 attendees who command most of the big resorts on the strip.

Yesterday I participated in a Security Certification Bootcamp (proper name AWS Certification Exam Readiness: Security – Specialty) and this morning I wrote the certification exam proper; three hours long, 65 questions, and I had 3 minutes to spare at the end. Let’s face it, the exam is hard, and requires studying. I was successful, but it required steady studying over the last 3 months. The AWS certification exams are challenging, but one does learn a lot. As an academic the hardness of the exams is a good thing as it says that this material has a legitimate role to play in academia, especially as we make it accessible to our students, and deploy it toward our research.

How did I prepare? In addition to reading the requisite white papers (such as Introduction to AWS Security Processes and AWS Best Practices for DDoS Resiliency), I was fortunate enough to have access to the Cloud Guru training in security. Their 10 to 15 minute lessons in all the topics are easy to absorb, and the summaries and quizzes are a good preparation for the exam.

I have been teaching Cybersecurity for over a decade, but the AWS security exam is not about foundations of Cybersecurity — it is about how to use AWS tools in order to achieve security objectives; this kind of knowledge arises not from learning principles or cryptography (although that does help too!), but rather from in-depth familiarity with AWS tools, such as CloudTrail, Inspector, Macie, Athena, CloudWatch, KMS, and many many others. My plan now is to incorporate this knowledge into our CI class in Cybersecurity, COMP 524, so that students will have knowledge of fundamentals as well as an understanding of security in the (relatively new) paradigm of cloud computing. COMP 524 students will have the additional benefit of covering the content of the certification

I should also say that even though foundational knowledge such as cryptography is not tested directly, it is nevertheless helpful. For example, a good portion of the exam relates to keys, specifically AWS KMS. It is much easier to remember when symmetric keys are used (e.g., S3 encryption with AES256) rather than asymmetric keys (i.e., public keys, e.g., key pairs to SSH into EC2) when one actually understand the difference between the two. Or, for example, why hashing of encrypted logs in S3 can help with data integrity measures for backups.

The Bootcamp that I took the day before was perhaps the least helpful toward success in the exam. I would suggest to take the bootcamp at the beginning of your studies toward passing the certification exam, as a quick bird-eye overview of what needs to be mastered. I sat through the bootcamp listening to what I knew already, without the possibility of going more in depth (we had 4 hours total), and without the audience being able to ask questions, as the instructor was rushing to cover the material.

Quick Tip: AWS is uncanny in its rolling out of new tools and features, most really captivating and useful. However, keep in mind that a tool or feature that is younger than 6 months will likely not make it to the exam. As I understand, the exam process is too exacting to be done quickly, and hence it take some time before new material is incorporated.

AWS update

Recently, Computer Science at CI, has made several new connections with AWS:

  • We are an approved member of the AWS Academy and we are authorized to deliver the AWS Academy Cloud Computing Architecture curriculum. I am the Central Point of Contact (CPOC), so if anyone is interested in being nominated to be an AWS Academy instructor at CI, please get in touch with me. [letter]
  • We are part of the AWS Educate initiative, and we were able to offer our COMP 529 students accounts with some credit. Note that an issue with AWS training accounts is that they close after the course is finished; to those students who are able, I would suggest to open your own (or your company’s) account so that as you learn the material you can build your own permanent infrastructure. A compromise is to build the initial infrastructure on a training account, and use “CloudFormation” to export it for re-instatement elsewhere.
  • Almost finished teaching COMP 529, “Cloud Computing,” for the first time using the AWS resources. We used the AWS Certified Solutions Architect official study guide .
  • I have been selected for the AWS Cloud Ambassador program, which offers educators recognition, professional development, and exclusive benefits for helping students learn about the cloud.
  • I have completed by own AWS certification as a Solutions Architect.