dns-ready

README

DNS Ready

Sometimes we just need to wait until a hostname is resolvable in DNS.

• This will repeatedly attempt to resolve a hostname and then exit gracefully if the DNS lookup is successful, or when the maximum number of attempts is reached.

• TERM and INT signals will cause immediate graceful exit.

• Graceful exit means ending the program with return code zero.

Configuration:

Options can be configured using command line flags, or DNSREADY_* environment variables:

Flag	Environment variable	Default	Description
-acceptempty	DNSREADY_ACCEPTEMPTY	false	Accept a DNS response with no IP addresses
-host	DNSREADY_HOST	kube-dns.kube-system.svc.cluster.local	The hostname to resolve
-pause	DNSREADY_PAUSE	800	Milliseconds to sleep between attempts
-timeout	DNSREADY_TIMEOUT	1200	Timeout in milliseconds for each DNS lookup attempt
-retries	DNSREADY_RETRIES	30	Maximum number of attempts before graceful exit
-success	DNSREADY_SUCCESS	2	Minimum successful resolutions before graceful exit
-exitcode	DNSREADY_EXITCODE	false	Exit with non-zero status code if unsuccessful
-verbose	DNSREADY_VERBOSE	false	Show each attempt on STDOUT
-silent	DNSREADY_SILENT	false	Do not show anything on STDOUT

Use as a Kubernetes "init container":

This can be used as an init container in Kubernetes to ensure any containers that depend on DNS are not started until DNS is really available.

apiVersion: apps/v1
kind: Deployment
spec:
  template:
    spec:
      initContainers:
      - name: dns-ready
        image: jamesjj/dns-ready
      containers:
      - ...
        ...