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Using Multicast-DNS mDNS, 2.3. Using DNS Round Robin

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2.2.2. Using Multicast-DNS (mDNS) Another way to make your nodes available on the network and of finding an initial PAN is to use mDNS. mDNS is often referred to by the name Zeroconf, the collective name form DNS and DNS Service Discovery to enable zero-configuration networking. mDNS is supported for all deployments and provides the most flexibility because it provides applications with a list of storage nodes to choose from when selecting a PAN without requiring the application to maintain a static list of IP addresses. Every DX Storage node implements an mDNS service that allows applications to do what is called service discovery. Even if DHCP is being used to assign and change node IP addresses, mDNS will allow an application to "discover" an active node in any DX Storage cluster and use it as the PAN. There are several free mDNS client implementations in various languages that application integrators may wish to reference when considering using mDNS node location. Note When you are using mDNS, make sure the value of the cluster parameter is unique for each cluster. The cluster parameter is located in the node.cfg file for a non-CSNmanaged cluster or in the PXE configuration for a CSN-managed cluster. DX Storage's mDNS support allows an application to discover all nodes on a network, all nodes in a specific cluster, or to look up a node. To do this it "publishes" several different records, including an A (host) record for the node and an SRV (service) record under the service type _scsp._tcp. Although a thorough discussion of mDNS and its use is beyond the scope of this document, a typical usage example follows. The example uses Avahi's command line tools to pass in the name of the cluster and return all nodes discovered in that cluster: % avahi-browse -tr _._sub._scsp._tcp local + eth0 IPv4 D2024267FF8F1DD056EEA15E40EE52C9 local = eth0 IPv4 CD35B28FD2E70CD1E47095C774F8050F local hostname = [CD35B28FD2E70CD1E47095C774F8050F.local] address = [192.168.1.123] port = [80] txt = [] = eth0 IPv4 D2024267FF8F1DD056EEA15E40EE52C9 local hostname = [D2024267FF8F1DD056EEA15E40EE52C9.local] address = [192.168.1.125] port = [80] txt = [] _scsp._tcp _scsp._tcp _scsp._tcp Here two nodes were found and their IP addresses were returned in the address field for each record. 2.2.3. Using DNS Round Robin For large and/or dynamic DX Storage clusters where nodes are being added and removed often, even for temporary maintenance reasons, you should address the cluster using a DNS host name instead of an IP address. Copyright © 2010 Caringo, Inc. All rights reserved 10 Version 5.0 December 2010

Section	Page
DX Object Storage Application Guide	1
Table of Contents	3
Chapter 1. Introduction to DX Storage Objects	6
1.1. Introducing Named Objects	6
1.2. Summary of Named Objects and Unnamed Objects	7
1.3. Common Named Object Terminology	7
1.4. About DX Storage Object Types	8
1.5. Bucket and Object Naming Rules	8
1.6. Simple Examples of Creating Buckets and Named Objects	8
1.7. Universal Resource Identifiers (URIs)	9
1.8. About Objects and Security	10
1.8.1. The Basics of DX Storage Security	10
1.8.2. Commonly Used Security Terminology	11
1.8.3. Basic Security Guidelines	11
1.9. Concepts for Unnamed Objects	11
1.9.1. Universally Unique Identifiers (UUIDs)	11
1.9.2. About Immutable Objects	12
1.9.3. About Anchor Streams	12
1.10. Document Typographical Conventions	13
Chapter 2. Connecting to a DX Storage Cluster	14
2.1. About the Primary Access Node (PAN)	14
2.2. Requirements for Node Accessibility	14
2.2.1. Using the DX Storage Software Development Kit (SDK)	14
2.2.2. Using Multicast-DNS (mDNS)	15
2.2.3. Using DNS Round Robin	15
2.2.4. Using a Pool of Static IP Addresses	16
2.2.5. Using a Single Static IP Address	16
Chapter 3. Application Best Practices	17
3.1. Using the Software Development Kit (SDK)	17
3.2. Dynamically Locating DX Storage Nodes	17
3.3. Optimizing Bucket and Domain Operations	17
3.4. Using HTTP Client Libraries	17
3.5. Handling Redirects	18
3.6. Using Range Headers	18
3.7. Multi-Threading	19
3.8. Using Persistent Connections	19
Chapter 4. Introduction to the Simple Content Storage Protocol (SCSP)	20
4.1. Mapping SCSP Operations to HTTP Methods	20
4.2. HTTP Overview	21
4.3. Requests and Responses	21
4.3.1. HTTP Response Codes	21
4.3.2. Redirect Responses	22
4.4. Formatting SCSP Commands for Named and Unnamed Objects	22
4.5. Undefined Responses from DX Storage	23
4.6. Normal Response Headers	24
Chapter 5. SCSP READ	27
5.1. Introduction to READ	27
5.1.1. Reading With Content Validation	27
5.1.2. Requestion Node Status and Cluster Capacity	27
5.2. Unnamed Object READ Details	28
5.3. Normal Responses to READ	28
5.3.1. Normal READ Responses for Named Objects	28
5.3.1.1. Normal READ Response for a Domain	28
5.3.1.2. Normal READ Response for a Bucket	29
5.3.1.3. Normal READ Response for a Named Object	29
5.3.2. Normal READ Response for Unnamed Objects	29
5.3.3. Other Normal READ Responses	30
5.4. Error Responses to READ	30
Chapter 6. SCSP WRITE	32
6.1. Introduction to WRITE	32
6.1.1. About the Expect: 100-continue Header and WRITE	33
6.1.2. About Replicate On Write	33
6.2. Named Object WRITE Details	33
6.3. Unnamed Object WRITE Details	33
6.4. Normal Responses to WRITE	33
6.5. Error Responses to WRITE	34
Chapter 7. SCSP DELETE	36
7.1. Introduction to DELETE	36
7.2. Unnamed Object DELETE Details	37
7.3. Named Object DELETE Details	37
7.4. Normal Responses to DELETE	37
7.5. Error Responses to DELETE	38
Chapter 8. SCSP UPDATE	39
8.1. Introduction to UPDATE	39
8.2. Unnamed Object UPDATE Details	39
8.3. Normal Responses to UPDATE	40
Chapter 9. SCSP COPY	41
9.1. Introduction to COPY	41
9.2. Unnamed Object COPY Details	41
9.3. Normal Responses to COPY	41
Chapter 10. SCSP APPEND	42
10.1. Introduction to APPEND	42
10.2. Unnamed Object APPEND Details	43
10.3. Normal Responses to APPEND	43
Chapter 11. SCSP INFO	44
11.1. Introduction to INFO	44
11.1.1. Getting Replica Counts	44
11.1.2. Getting Node Status and Cluster Capacity	44
11.2. Unnamed Object INFO Details	45
11.3. Normal Responses to INFO	45
11.3.1. Normal INFO Responses for Named and Unnamed Objects	45
11.3.2. Normal INFO Responses for Named Objects	46
11.3.3. Normal INFO Responses for Unnamed Objects	47
11.4. Error Responses to INFO	47
Chapter 12. Introduction to Object Security	48
12.1. About Security Roles	48
12.2. Security Realm Overview	49
12.2.1. Common Security Terminology	49
12.2.2. About Security Realms	49
12.2.3. About Realm Caching and Security	49
12.3. About Authorization Header Syntax	50
12.3.1. About Realm Names	51
12.3.1.1. About Realms and Buckets	51
12.3.1.2. About owner@ and @owner Syntax	51
12.3.1.3. About user@realm Syntax	51
12.4. Authorization Specification Examples	51
12.5. About Authorization Header Evaluation	52
12.6. Creating Realms	53
12.7. Updating the Realm on a Bucket	54
12.8. Administrative Override and Security	54
Chapter 13. Managing Security for Application Developers	55
13.1. What Application Developers Need to Know	55
13.2. About Bucket Authorization	55
13.3. Example: Creating Bucket Owners	56
13.4. Examples of Creating Buckets and Named Objects	56
Chapter 14. Managing Security for Domain Managers	59
14.1. What Domain Managers Need to Know	59
14.2. About Domain Manager Tasks and Responsibilities	59
14.3. Examples of Updating Domain and Administrator User Lists	59
14.3.1. Updating the Domain Realm	60
14.3.2. Updating the Domain Manager Realm	61
14.3.3. Updating a Realm Using PUT	62
Chapter 15. Using the Content-MD5 Metadata Header	64
Chapter 16. Using Lifepoint Metadata Headers	65
16.1. About Storage Policies	65
16.2. A Simple Lifecycle Example	65
16.3. Lifepoint/Lifecycle Specification	66
16.4. Constraint Types	66
16.4.1. Replication	67
16.4.2. Deletion	67
Chapter 17. Using the Allow Metadata Header	69
17.1. Overview of the Allow Header	69
17.2. Administrative Override	69
Chapter 18. Using Caching Metadata Headers	71
18.1. About Caching Headers	71
18.2. Using HTTP/1.0 Caching Headers	71
18.2.1. Last-Modified	71
18.2.2. If-Modified-Since	71
18.2.3. If-Unmodified-Since	71
18.2.4. Expires	72
18.3. Using HTTP/1.1 Caching Headers	72
18.3.1. ETag	72
18.3.2. If-Match	72
18.3.3. If-None-Match	73
18.3.4. If-Range	73
Chapter 19. Using Custom Metadata Headers	75
Chapter 20. Basic Content Integrity Assurance	76
20.1. Integrity Seals	76
20.2. Validating Reads	76
20.3. Application Initiated Hash Upgrading	77
Appendix A. Content Header Metadata	78
Appendix B. Sample Code and Client Library Behaviors with 100-Continue	80

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Version 5.0

December 2010

2.2.2. Using Multicast-DNS (mDNS)

Another way to make your nodes available on the network and of finding an initial PAN is to use

mDNS. mDNS is often referred to by the name

Zeroconf

, the collective name form DNS and DNS

Service Discovery to enable zero-configuration networking.

mDNS is supported for all deployments and provides the most flexibility because it provides

applications with a list of storage nodes to choose from when selecting a PAN without requiring the

application to maintain a static list of IP addresses.

Every DX Storage node implements an mDNS service that allows applications to do what is called

service discovery. Even if DHCP is being used to assign and change node IP addresses, mDNS

will allow an application to “discover” an active node in any DX Storage cluster and use it as the

PAN. There are several free mDNS client implementations in various languages that application

integrators may wish to reference when considering using mDNS node location.

Note

When you are using mDNS, make sure the value of the

cluster

parameter is unique

for each cluster. The

cluster

parameter is located in the

node.cfg

file for a non-CSN-

managed cluster or in the PXE configuration for a CSN-managed cluster.

DX Storage’s mDNS support allows an application to discover all nodes on a network, all nodes in a

specific cluster, or to look up a node. To do this it “publishes” several different records, including an

A (host) record for the node and an SRV (service) record under the service type

_scsp._tcp

Although a thorough discussion of mDNS and its use is beyond the scope of this document, a

typical usage example follows. The example uses Avahi's command line tools to pass in the name

of the cluster and return all nodes discovered in that cluster:

% avahi-browse -tr _<clustername>._sub._scsp._tcp

local

+ eth0 IPv4 D2024267FF8F1DD056EEA15E40EE52C9

_scsp._tcp

local

= eth0 IPv4 CD35B28FD2E70CD1E47095C774F8050F

_scsp._tcp

local

hostname = [CD35B28FD2E70CD1E47095C774F8050F.local]

address = [192.168.1.123]

port = [80]

txt = []

= eth0 IPv4 D2024267FF8F1DD056EEA15E40EE52C9

_scsp._tcp

local

hostname = [D2024267FF8F1DD056EEA15E40EE52C9.local]

address = [192.168.1.125]

port = [80]

txt = []

Here two nodes were found and their IP addresses were returned in the address field for each

record.

2.2.3. Using DNS Round Robin

For large and/or dynamic DX Storage clusters where nodes are being added and removed often,

even for temporary maintenance reasons, you should address the cluster using a DNS host name

instead of an IP address.