cluster.go

/*
Copyright 2014 Rohith All rights reserved.

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

    http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
*/

package marathon

import (
	"fmt"
	"net/http"
	"net/url"
	"strings"
	"sync"
	"time"
)

const (
	memberStatusUp   = 0
	memberStatusDown = 1
)

// the status of a member node
type memberStatus int

// cluster is a collection of marathon nodes
type cluster struct {
	sync.RWMutex
	// a collection of nodes
	members []*member
	// the http client
	client *http.Client
}

// member represents an individual endpoint
type member struct {
	// the name / ip address of the host
	endpoint string
	// the status of the host
	status memberStatus
}

// newCluster returns a new marathon cluster
func newCluster(client *http.Client, marathonURL string) (*cluster, error) {
	// step: extract and basic validate the endpoints
	var members []*member
	var defaultProto string

	for _, endpoint := range strings.Split(marathonURL, ",") {
		// step: check for nothing
		if endpoint == "" {
			return nil, newInvalidEndpointError("endpoint is blank")
		}
		// step: parse the url
		u, err := url.Parse(endpoint)
		if err != nil {
			return nil, newInvalidEndpointError("endpoint: %s is invalid reason: %s", endpoint, err)
		}
		// step: set the default protocol schema
		if defaultProto == "" {
			if u.Scheme != "http" && u.Scheme != "https" {
				return nil, newInvalidEndpointError("endpoint: %s protocol must be (http|https)", endpoint)
			}
			defaultProto = u.Scheme
		}
		// step: does the url have a protocol schema? if not, use the default
		if u.Scheme == "" || u.Opaque != "" {
			urlWithScheme := fmt.Sprintf("%s://%s", defaultProto, u.String())
			if u, err = url.Parse(urlWithScheme); err != nil {
				panic(fmt.Sprintf("unexpected parsing error for URL '%s' with added default scheme: %s", urlWithScheme, err))
			}
		}

		// step: check for empty hosts
		if u.Host == "" {
			return nil, newInvalidEndpointError("endpoint: %s must have a host", endpoint)
		}

		// step: create a new node for this endpoint
		members = append(members, &member{endpoint: u.String()})
	}

	return &cluster{
		client:  client,
		members: members,
	}, nil
}

// retrieve the current member, i.e. the current endpoint in use
func (c *cluster) getMember() (string, error) {
	c.RLock()
	defer c.RUnlock()
	for _, n := range c.members {
		if n.status == memberStatusUp {
			return n.endpoint, nil
		}
	}

	return "", ErrMarathonDown
}

// markDown marks down the current endpoint
func (c *cluster) markDown(endpoint string) {
	c.Lock()
	defer c.Unlock()
	for _, n := range c.members {
		// step: check if this is the node and it's marked as up - The double  checking on the
		// nodes status ensures the multiple calls don't create multiple checks
		if n.status == memberStatusUp && n.endpoint == endpoint {
			n.status = memberStatusDown
			go c.healthCheckNode(n)
			break
		}
	}
}

// healthCheckNode performs a health check on the node and when active updates the status
func (c *cluster) healthCheckNode(node *member) {
	// step: wait for the node to become active ... we are assuming a /ping is enough here
	for {
		res, err := c.client.Get(fmt.Sprintf("%s/ping", node.endpoint))
		if err == nil && res.StatusCode == 200 {
			break
		}
		<-time.After(time.Duration(5 * time.Second))
	}
	// step: mark the node as active again
	c.Lock()
	defer c.Unlock()
	node.status = memberStatusUp
}

// activeMembers returns a list of active members
func (c *cluster) activeMembers() []string {
	return c.membersList(memberStatusUp)
}

// nonActiveMembers returns a list of non-active members in the cluster
func (c *cluster) nonActiveMembers() []string {
	return c.membersList(memberStatusDown)
}

// memberList returns a list of members of a specified status
func (c *cluster) membersList(status memberStatus) []string {
	c.RLock()
	defer c.RUnlock()
	var list []string
	for _, m := range c.members {
		if m.status == status {
			list = append(list, m.endpoint)
		}
	}

	return list
}

// size returns the size of the cluster
func (c *cluster) size() int {
	return len(c.members)
}

// String returns a string representation
func (m member) String() string {
	status := "UP"
	if m.status == memberStatusDown {
		status = "DOWN"
	}

	return fmt.Sprintf("member: %s:%s", m.endpoint, status)
}