# Placing an R Lambda Runtime in a Container

Consider the following `runtime.R` file:

    parity <- function(number) {
      list(parity = if (as.integer(number) %% 2 == 0) "even" else "odd")
    }

    lambdr::start_lambda()

The `parity` function accepts a `number` argument and returns its parity as a named list, for example:

    parity(5)
    # $parity
    # [1] "odd"

    parity(8)
    # $parity
    # [1] "even"

This function can then be placed into a Docker image. An example is provided below, but the key components are:

- Start from the `public.ecr.aws/lambda/provided:al2` parent image, which provides the basic components necessary to serve a Lambda
- Install R and dependencies, both system dependencies and R packages, including the `lambdr` package
- Copy across `runtime.R` and any other necessary files
- Generate a simple bootstrap which runs `runtime.R` with R
- Set the handler as the `CMD`. The `lambdr` package interprets the handler as the name of the function to use, in this case, “parity”. The `CMD` can also be set (or overriden) when setting up the Lambda in AWS.

    FROM public.ecr.aws/lambda/provided:al2

    ENV R_VERSION=4.0.3

    RUN yum -y install wget git tar

    RUN yum -y install https://dl.fedoraproject.org/pub/epel/epel-release-latest-7.noarch.rpm \
      && wget https://cdn.rstudio.com/r/centos-7/pkgs/R-${R_VERSION}-1-1.x86_64.rpm \
      && yum -y install R-${R_VERSION}-1-1.x86_64.rpm \
      && rm R-${R_VERSION}-1-1.x86_64.rpm

    ENV PATH="${PATH}:/opt/R/${R_VERSION}/bin/"

    # System requirements for R packages
    RUN yum -y install openssl-devel

    RUN Rscript -e "install.packages(c('httr', 'jsonlite', 'logger', 'remotes'), repos = 'https://packagemanager.rstudio.com/all/__linux__/centos7/latest')"
    RUN Rscript -e "remotes::install_github('mdneuzerling/lambdr')"

    RUN mkdir /lambda
    COPY runtime.R /lambda
    RUN chmod 755 -R /lambda

    RUN printf '#!/bin/sh\ncd /lambda\nRscript runtime.R' > /var/runtime/bootstrap \
      && chmod +x /var/runtime/bootstrap

    CMD ["parity"]

The image is built and uploaded to AWS Elastic Container Registry (ECR). First, a repository is created:

    aws ecr create-repository --repository-name parity-lambda --image-scanning-configuration scanOnPush=true

This provides a URI, the resource identifier of the created repository. The image can now be pushed:

    docker tag mdneuzerling/r-on-lambda:latest {URI}/parity-lambda:latest
    aws ecr get-login-password | docker login --username AWS --password-stdin {URI}
    docker push {URI}/parity-lambda:latest

In either the AWS console or the command line, a Lambda can be created from this image. Call the Lambda “parity” to match the function name. Tests can be executed within the console. Alternatively the Lambda can be invoked from the CLI:

    aws lambda invoke --function-name parity \
      --invocation-type RequestResponse --payload '{"number": 8}' \
      /tmp/response.json --cli-binary-format raw-in-base64-out

The output is now available in the generated file:

    cat /tmp/response.json

    {"parity":"even"}