Port offset

Table of contents

• Introduction
• How the offset is applied
• Declaring a port in your feature
• See also

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Introduction

Every product shifts the host ports of its features by an amount derived from its name, so several products run on one machine without collisions. The shift is the same on every run, so your ports never move.

  ports    adjusted 4 feature port(s) (+591)

That is product:env --merge in my_first_app, whose offset is 591.

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How the offset is applied

Both products run Redis at once, each on its own host port. A port the product sets itself is used as written.

offset = crc32(product_name.encode("utf-8")) % 1000

product:env --merge and product:build add the offset to every feature port, a numeric variable whose name ends in _HOST_PORT or contains _PORT_ONE or _PORT_TWO. A port your product sets itself, in its env file or its [tool.splent.config], is used as written. The features’ own files and your product’s ports, such as the web server’s, are never touched.

Server	Variable	Base port	In my_first_app
A cache	REDIS_HOST_PORT	6380	6971
A database UI	DBUI_HOST_PORT	8081	8672
A mail catcher, SMTP	MAILCATCHER_SMTP_HOST_PORT	1025	1616
A mail catcher, web UI	MAILCATCHER_UI_HOST_PORT	8025	8616

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Declaring a port in your feature

Name the variable with a _HOST_PORT suffix, give it a base value away from common system ports in docker/.env.example, and use it in the compose file.

PROXY_HTTP_HOST_PORT=8088

ports:
  - "${PROXY_HTTP_HOST_PORT}:80"

Features that run a server has the rest of the rules.

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See also

• product:env --merge and product:build, which apply the offset