dali

dali (named after the great painter Salvador Dali) is a service which performs image transformations. It is used by OLX to process and serve images for users in around 40 countries. The application supports:

• Retrieving source images from an HTTP URL
• Encoding images to PNG, JPEG, WEBP or HEIC
• Resizing an image
• Rotating an image
• Apply a watermark image to an image

Configuration

All configuration should be provided through either a json config file or environment variables. The application will search first by a file named config/default.json, then if the environment variable RUN_MODE is set it will search for config/RUN_MODE, override the values and lastly it will override with environment variables.

Name	Type	Description	Required	Possible Values	Notes
log_level	Enum(trace, debug, info, warn, error)	Logging level for the application	N	error warn info debug trace	Default value is info.
app_port	integer	Port which the web server listens to for requests	Y	-
health_port	integer	Port which the web server listens to for the health requests	Y	-
vips_threads	integer	Max number of threads for image processing that will be used	N	-	if not specified it will take num_of_cpus/2 with a minimum of 1
reqwest_timeout_millis	integer	Only applicable when running Dali with the reqwest feature which implies that the images that have to be processed are stored behind an http server and will be download with a Reqwest client. Enables a request timeout for the Reqwest client. The timeout is applied from when the request starts connecting until the response body has finished.	N (only in reqwest mode)	-	if not specified, the default is 2000 milliseconds
reqwest_connection_timeout_millis	integer	Only applicable when running Dali with the reqwest feature which implies that the images that have to be processed are stored behind an http server and will be downloaded with a Reqwest http client. Set a timeout for only the connect phase of a Client.	N (only in reqwest mode)	-	if not specified, the default is 2000 milliseconds
reqwest_pool_max_idle_per_host	integer	Only applicable when running Dali with the reqwest feature which implies that the images that have to be processed are stored behind an http server and will be downloaded with a Reqwest http client. Sets the maximum idle connection per host allowed in the pool.	N (only in reqwest mode)	-	if not specified, the default is 10 connections
reqwest_pool_idle_timeout_millis	integer	Only applicable when running Dali with the reqwest feature which implies that the images that have to be processed are stored behind an http server and will be downloaded with a Reqwest http client. Set an optional timeout for idle sockets being kept-alive.	N (only in reqwest mode)	-	if not specified, the default is 60000 milliseconds
s3_region	String	Only applicable when running Dali with the s3 feature which implies that the images that have to be processed are stored in an S3 bucket. The region where the bucket resides.	Y (only in S3 mode)	-	if not provided, Dali panics while trying to instantiate the S3 client
s3_key	String	Only applicable when running Dali with the s3 feature which implies that the images that have to be processed are stored in an S3 bucket. The key of an AWS IAM user configured for programatic access to download the images from S3.	N (only in S3 mode)	-	if not provided together with the s3_secret, the S3 client tries to instantiate the S3 client based on the enviroment variables
s3_secret	String	Only applicable when running Dali with the s3 feature which implies that the images that have to be processed are stored in an S3 bucket. The secret of an AWS IAM user configured for programatic access to download the images from S3.	N (only in S3 mode)	-	if not provided together with the s3_key, the S3 client tries to instantiate the S3 client based on the enviroment variables
s3_endpoint	String	Only applicable when running Dali with the s3 feature which implies that the images that have to be processed are stored in an S3 bucket. This configuration property is only needed for the local dev environment where MinIO is used to emulate S3.	N (only in S3 mode)	-	it's only needed when wanting to use MinIO for the local development environment. has to be ommited when using Dali in production with the real S3
s3_bucket	String	Only applicable when running Dali with the s3 feature which implies that the images that have to be processed are stored in an S3 bucket. The name of the S3 bucket from where Dali will download the images that need processing.	Y (only in S3 mode)	-	if not provided Dali panics while trying to instantiate the S3 client
max_file_size	integer	Maximum allowed size for the file to be processed. If the file size exceeds this limit, the download will be aborted.	N	-	if not provided, Dali will not check the file size

The application will compute the number of threads by the following formula: pod_number_of_cpus * cpu_usage_percentage / 100. This number will be divided by 2 and half will be assigned to the HTTP connection listener and half will be assigned to libvips (the image library). An extra worker will be created to listen to the health endpoint (this was done to be sure the application won't block the health endpoint even when overloaded).

Running locally

Requirements

• Libvips
• A HTTP server for images
• Docker
• Rust (1.74.0)

This application relies on C libvips library. That means it has to be previously installed into the system before compiling and/or running.

For installation follow this instructions. (Required minimum version 8.10.1)

Using rustup is the recommended way to install rust. It is a tool that manages and updates rust versions (like nvm for node for example). To install it, simply run curl --proto '=https' --tlsv1.2 -sSf https://sh.rustup.rs | sh. Then run rustup install 1.74.0.

To build and run the application, run the following command:

cargo run

Note: if you're building the application on a linux musl system, you'll need to set this env variable: RUSTFLAGS='-C target-feature=-crt-static' if it fails to compile because of the linker, try to add the result of pkg-config --libs vips to RUSTFLAGS= env variable`

Local development environment

• dev-env.start locally starts a MinIO server inside a docker container. This server acts as both an HTTP server and an S3 emulator. This is achieved by having two buckets that both contain the same test-image.jpeg file:

1. dali-public which is publicly avaialble hence the image can be fetched over http using the following url: http://localhost:2969/dali-public/test-image.jpeg
2. dali-private which can only be accesed by the dummy credentials present within the default.json config file.

• dev-env.stop stops the MinIO server that runs locally.

Testing

There are 3 kinds of tests: unit, integration and benchmark tests.

Unit Tests

At the moment, the only logic the application has is regarding resizing and watermark positioning. There are some unit tests around these use cases in the package image_processor. All other functions are deeply tied to the libvips library which complicates testing since it is not easily mockable. To run them, simply execute: cargo test --bin dali. The parameter --bin is needed because otherwise it would run also integration tests.

Integration Tests

This tests run over a running application. To run the tests, the script will start the containers through docker-compose, copy some sample files to the http container and run the tests over the application, checking the array of bytes from the responses against expected result images stored in the tests/resources/results directory. To run the whole flow, simply run: make test.

Benchmark Tests

This is an experimental feature from rust, so in order to use, the nightly rust toolchain has to be enabled. To do that run:

rustup toolchain install nightly
rustup default nightly

To rollback to stable, run rustup default stable.

To run the benchmark, simply call cargo bench (application must be running at localhost on port 8080).

It outputs the average time per iteration and the deviation between max and min. Example output from a 4 core 2.3GHz MacBook (application running inside docker limited to 4 cores and with 4 workers):

test bench_highhes ... bench: 71,112,344 ns/iter (+/- 7,798,699)

API

The application supports the following endpoints.

/health

Signifies the application is healthy by returning a HTTP Status OK - 200 return code.

/metrics

Prometheus formatted metrics. Currently exposes request count and duration per endpoint

/

Fetches and processes an image file. The only mandatory parameter is the image_address.

General query parameters

Parameter	Description
image_address	The address for the Image. Should be a HTTP, HTTPS or HTTP valid URI.
format	desired image format. Possible values are Jpeg, Png, Heic and Webp. Defaults to Jpeg
quality	desired quality for the image. For Jpeg, it goes from 0 to 100 (defaults to 75)
size[width]	desired width for the image. Images won't get upscaled or have their aspect ratio changed by variations on parameters for width and height.
size[height]	desired height for the image. Images won't get upscaled or have their aspect ratio changed by variations on parameters for width and height.
rotation	optional rotation of the image. Possible values are R90, R180 and R270

Watermarking query parameters

Watermarks is an array parameter and therefore, must be indexed when informed (0 indexed).

Parameter	Description
watermarks[0][image_address]	watermark file. File has to be smaller than original file. Should be a HTTP, HTTPS or HTTP valid URI.
watermarks[0][alpha]	opacity from the watermark over the original image. it is a floating point number from 0 to 1.
watermarks[0][position][x][origin]	identifier to position the watermark based on a point or centered (X axis). Possible values: Left (default), Right, Center.
watermarks[0][position][y][origin]	identifier to position the watermark based on a point or centered (Y axis). Possible values: Top (default), Bottom, Center.
watermarks[0][position][x][pos]	position of the watermark in the X axis. Value in pixels.
watermarks[0][position][y][pos]	position of the watermark in the Y axis. Value in pixels.
watermarks[0][size]	optional size of the watermark. It should be a value between 1 and 100 representing a percentage from the original image.

License

(c) Copyright 2019-2024 OLX. Released under Apache 2 License