agent/app/agent.go
func (agent *ecsAgent) verifyRequiredDockerVersion() (int, bool) {
	supportedVersions := agent.dockerClient.SupportedVersions()
	if len(supportedVersions) == 0 {
		seelog.Critical("Could not get supported docker versions.")
		return exitcodes.ExitError, false
	}

	// if api version 1.21 is supported, it means docker version is at least 1.9.0
	for _, version := range supportedVersions {
		if version == dockerclient.Version_1_21 {
			return -1, true
		}
	}

	// api 1.21 is not supported, docker version is older than 1.9.0
	seelog.Criticalf("Required minimum docker API verion %s is not supported",
		dockerclient.Version_1_21)
	return exitcodes.ExitTerminal, false
}
func (agent *ecsAgent) verifyRequiredDockerVersion() (int, bool) {
	supportedVersions := agent.dockerClient.SupportedVersions()
	if len(supportedVersions) == 0 {
		seelog.Critical("Could not get supported docker versions.")
		return exitcodes.ExitError, false
	}

	// if api version 1.21 is supported, it means docker version is at least 1.9.0
	for _, version := range supportedVersions {
		if version == dockerclient.Version_1_21 {
			return -1, true
		}
	}

	// api 1.21 is not supported, docker version is older than 1.9.0
	seelog.Criticalf("Required minimum docker API verion %s is not supported",
		dockerclient.Version_1_21)
	return exitcodes.ExitTerminal, false
}
// validateRequiredVersion validates docker version.
// Minimum docker version supported is 1.9.0, maps to api version 1.21
// see https://docs.docker.com/develop/sdk/#api-version-matrix