Use a plumber Microservice in an R Project

Lay the infrastructure for a microservice. That includes unit test, dependency packages, configuration file, entrypoints and utility endpoint.

use_microservice(path = ".", overwrite = FALSE)

Arguments

path	(character) Where is the project root folder?
overwrite	(logical) Should existing destination files be overwritten?

Value

No return value, called for side effects.

Details

How It Works

Given a path to a folder

When use_microservice(path = ".") is called

Then the function creates the following files:

tests/testthat/test-endpoint-plumber-utility.R
inst/configurations/plumber.yml
inst/endpoints/plumber-utility.R
inst/entrypoints/plumber-background.R
inst/entrypoints/plumber-foreground.R

And updates the following files:

tests/testthat/helpers-xyz.R

And adds the following packages to the DESCRIPTION file:

type	package	version
Suggests	config	*
Suggests	httptest	*
Suggests	httr	*
Imports	jsonlite	*
Suggests	pkgload	*
Suggests	plumber	>= 1.0.0
Imports	purrr	*
Suggests	testthat	*
Suggests	usethis	*
Suggests	promises	*
Suggests	future	*

When to Use plumber

• A Single user/machine applications.

• Scheduled tasks. For example, you could use AirFlow with HTTP Operators to automate processes.

plumber Advantages

• Comes with familiar way to document the microservice endpoint.

• Maturing package that comes with documentation, examples and support.

plumber Disadvantages

• Runs on a single thread. That means that parallel algorithms such as random forest, can only be run on one core.

• Serves only one caller at a time.

• Can’t make inward calls for other services, That means plumber can’t be re-entrant. For example, if a microservice has three endpoints,read_table, write_table, and orchestrator, where the orchestrator reads a data table, transforms it, and writes it back, then the orchestrator can’t make inwards calls via HTTP to read_table and write_table.

Note: While plumber is single-threaded by nature, it is possible to perform parallel execution using the promises package. See links under References.

Workflow

1. Deploy the Microservice infrastructure

microservices::use_microservice(path = ".")
remotes::install_deps()
devtools::document()

1. Spin-up the microservice by running source("./inst/entrypoints/plumber-background.R")

2. Run the microservice unit-test by pressing Ctrl+Shift+T on Windows

Congratulations! You have added a microservice to your application and tested that it works.

References

• Parallel execution in plumber

• promises package

See also

Other plumber microservice: add_service()

Examples

path <- tempfile()
use_microservice(path)

list.files(path, recursive = TRUE)
#> [1] "DESCRIPTION"                                   
#> [2] "inst/configurations/plumber.yml"               
#> [3] "inst/endpoints/plumber-utility.R"              
#> [4] "inst/entrypoints/plumber-background.R"         
#> [5] "inst/entrypoints/plumber-foreground.R"         
#> [6] "tests/testthat/helpers-xyz.R"                  
#> [7] "tests/testthat/test-endpoint-plumber-utility.R"

cat(read.dcf(file.path(path, "DESCRIPTION"), "Imports"))
#> jsonlite,
#> purrr
cat(read.dcf(file.path(path, "DESCRIPTION"), "Suggests"))
#> config,
#> httptest,
#> httr,
#> pkgload,
#> plumber (>= 1.0.0),
#> testthat,
#> usethis,
#> promises,
#> future