gowait: a golang service waiter

Purpose

I started using Kubernetes often in my daily life and found a persistent irritation in waiting for scores of deployed pods to come up for local development. There are shell script-based solutions out there, and they work. However, shells in a production container are viewed as a security risk. To mitigate this, I wanted a statically-linked, single-file binary that could run in a very small container and give me the flexibility to configure it however I may need.

gowait is what I came up with. :)

Usage

Add the docker image as an InitContainer to your favourite deployment file and configure appropriately. I publish a pre-built image for each release here: https://hub.docker.com/repository/docker/neflyte/gowait

CLI Arguments

Usage

gowait -c|-configsource <env|yaml|json> [-f|-configfile <fileLocation>]

• -c | -configsource
  • Where to read app configuration from
  • Values:
    • env: environment variables (the default)
    • yaml: YAML file
    • json: JSON file
• -f | -configfile
  • Location of configuration file to read
  • Used when -configsource is set to yaml or json

Environment Variables

• GOWAIT_RETRY_DELAY
  • The amount of time to delay before retrying
  • Expressed as a string suitable for passing to time.ParseDuration()
  • e.g.: GOWAIT_RETRY_DELAY="15s"
• GOWAIT_RETRY_LIMIT
  • The maximum number of attempts to make
  • Expressed as a positive integer value greater than zero
  • e.g.: GOWAIT_RETRY_LIMIT="20"
• GOWAIT_URL
  • A URL representing the service to wait for
  • e.g.: GOWAIT_URL="postgres://user@localhost:5432/database?ssl_mode=disable"
  • Supported URL schemes:
    • postgres
      • Uses lib/pq to attempt a connection to a PostgreSQL database
    • tcp
      • Attempts a connection to a TCP port
      • If an established connection is alive for at least one second, the attempt succeeded
• GOWAIT_SECRET_SOURCE
  • Where to read the secret value from
  • e.g.: GOWAIT_SECRET_SOURCE="file"
  • Supported values:
    • env: environment variables (the default)
    • file: a file
• GOWAIT_SECRET_FILENAME
  • The name of the file to read the secret value from
  • Used when GOWAIT_SECRET_SOURCE="file"
  • e.g.: GOWAIT_SECRET_FILENAME="/tmp/secret.txt"
• GOWAIT_SECRET
  • The secret value
  • Used by default and when GOWAIT_SECRET_SOURCE="env"
  • e.g.: GOWAIT_SECRET="fnord"
• GOWAIT_LOG_FORMAT
  • The format of log messages
  • e.g.: GOWAIT_LOG_FORMAT="text"
  • Supported values:
    • text: Human-readable text (the default)
    • json: logstash-like JSON

YAML Configuration Example

---
url: "postgres://user@localhost:5432/database?ssl_mode=disable"
retryDelay: "15s"
retryLimit: 20
secretSource: "file"
secretFilename: "/tmp/secret.txt"
logFormat: "text"

JSON Configuration Example

{
  "url": "postgres://user@localhost:5432/database?ssl_mode=disable",
  "retryDelay": "15s",
  "retryLimit": 20,
  "secretSource": "file",
  "secretFilename": "/tmp/secret.txt",
  "logFormat": "text"
}