OpenLDAP2.4管理员指南
本文的英文原文来自OpenLDAP Software 2.4 Administrator's Guide
由于OpenLDAP2.4版的复制部分产生了重大变化，所以优先翻译这部分, OpenLDAP Software 2.4 Administrator's Guide : Replication
目录 |
复制
为了提供一个有弹性的企业部署，复制目录是一个基础需求.
OpenLDAP有多种配置选项来建立一个可复制的目录. 在前一个版本里面, 复制被限定在一个主服务器和若干个从服务器的条件下来讨论。一个主服务器从其他客户端接受目录更新, 而一个从服务器则仅仅从一个（单个的）主服务器接受更新. 这个复制结构被僵化地定义并且任何典型的数据库只能完成一个单一角色,主或者从.
现在OpenLDAP支持一个更广泛的复制拓扑, 关于提供者和消费者的以下这些条件已经不推荐了: 一个提供者复制目录更新到消费者; 消费者从提供者接收复制更新. 不像僵化定义的主/从关系,提供者/消费者角色更加的流动化：一个接收复制更新的消费者可能传递给其它服务器的另一个消费者，所以一个消费者也可以同时成为一个提供者。而且，消费者不需要成为一个实际上的LDAP服务器;它也可以仅仅是一个LDAP客户端。
以下章节将描述复制技术和讨论各种可用的复制选项.
复制技术
LDAP同步复制
LDAP同步复制引擎, 简称syncrepl, 是一个消费方的复制引擎，能让消费者服务器维护一个抽取片断的影子副本. 一个syncrepl引擎以slapd的一个线程的方式驻留在消费者那里. 它通过连接一个复制提供者来建立和维护一个消费者复制，It creates and maintains a consumer replica by connecting to the replication provider to perform the initial DIT content load followed either by periodic content polling or by timely updates upon content changes.
Syncrepl uses the LDAP Content Synchronization protocol (or LDAP Sync for short) as the replica synchronization protocol. LDAP Sync provides a stateful replication which supports both pull-based and push-based synchronization and does not mandate the use of a history store. In pull-based replication the consumer periodically polls the provider for updates. In push-based replication the consumer listens for updates that are sent by the provider in realtime. Since the protocol does not require a history store, the provider does not need to maintain any log of updates it has received. (Note that the syncrepl engine is extensible and additional replication protocols may be supported in the future.)
Syncrepl keeps track of the status of the replication content by maintaining and exchanging synchronization cookies. Because the syncrepl consumer and provider maintain their content status, the consumer can poll the provider content to perform incremental synchronization by asking for the entries required to make the consumer replica up-to-date with the provider content. Syncrepl also enables convenient management of replicas by maintaining replica status. The consumer replica can be constructed from a consumer-side or a provider-side backup at any synchronization status. Syncrepl can automatically resynchronize the consumer replica up-to-date with the current provider content.
Syncrepl supports both pull-based and push-based synchronization. In its basic refreshOnly synchronization mode, the provider uses pull-based synchronization where the consumer servers need not be tracked and no history information is maintained. The information required for the provider to process periodic polling requests is contained in the synchronization cookie of the request itself. To optimize the pull-based synchronization, syncrepl utilizes the present phase of the LDAP Sync protocol as well as its delete phase, instead of falling back on frequent full reloads. To further optimize the pull-based synchronization, the provider can maintain a per-scope session log as a history store. In its refreshAndPersist mode of synchronization, the provider uses a push-based synchronization. The provider keeps track of the consumer servers that have requested a persistent search and sends them necessary updates as the provider replication content gets modified.
With syncrepl, a consumer server can create a replica without changing the provider's configurations and without restarting the provider server, if the consumer server has appropriate access privileges for the DIT fragment to be replicated. The consumer server can stop the replication also without the need for provider-side changes and restart.
Syncrepl supports partial, sparse, and fractional replications. The shadow DIT fragment is defined by a general search criteria consisting of base, scope, filter, and attribute list. The replica content is also subject to the access privileges of the bind identity of the syncrepl replication connection.
LDAP内容同步协议
The LDAP Sync protocol allows a client to maintain a synchronized copy of a DIT fragment. The LDAP Sync operation is defined as a set of controls and other protocol elements which extend the LDAP search operation. This section introduces the LDAP Content Sync protocol only briefly. For more information, refer to RFC4533.
The LDAP Sync protocol supports both polling and listening for changes by defining two respective synchronization operations: refreshOnly and refreshAndPersist. Polling is implemented by the refreshOnly operation. The consumer polls the provider using an LDAP Search request with an LDAP Sync control attached. The consumer copy is synchronized to the provider copy at the time of polling using the information returned in the search. The provider finishes the search operation by returning SearchResultDone at the end of the search operation as in the normal search. Listening is implemented by the refreshAndPersist operation. As the name implies, it begins with a search, like refreshOnly. Instead of finishing the search after returning all entries currently matching the search criteria, the synchronization search remains persistent in the provider. Subsequent updates to the synchronization content in the provider cause additional entry updates to be sent to the consumer.
The refreshOnly operation and the refresh stage of the refreshAndPersist operation can be performed with a present phase or a delete phase.
In the present phase, the provider sends the consumer the entries updated within the search scope since the last synchronization. The provider sends all requested attributes, be they changed or not, of the updated entries. For each unchanged entry which remains in the scope, the provider sends a present message consisting only of the name of the entry and the synchronization control representing state present. The present message does not contain any attributes of the entry. After the consumer receives all update and present entries, it can reliably determine the new consumer copy by adding the entries added to the provider, by replacing the entries modified at the provider, and by deleting entries in the consumer copy which have not been updated nor specified as being present at the provider.
The transmission of the updated entries in the delete phase is the same as in the present phase. The provider sends all the requested attributes of the entries updated within the search scope since the last synchronization to the consumer. In the delete phase, however, the provider sends a delete message for each entry deleted from the search scope, instead of sending present messages. The delete message consists only of the name of the entry and the synchronization control representing state delete. The new consumer copy can be determined by adding, modifying, and removing entries according to the synchronization control attached to the SearchResultEntry message.
In the case that the LDAP Sync provider maintains a history store and can determine which entries are scoped out of the consumer copy since the last synchronization time, the provider can use the delete phase. If the provider does not maintain any history store, cannot determine the scoped-out entries from the history store, or the history store does not cover the outdated synchronization state of the consumer, the provider should use the present phase. The use of the present phase is much more efficient than a full content reload in terms of the synchronization traffic. To reduce the synchronization traffic further, the LDAP Sync protocol also provides several optimizations such as the transmission of the normalized entryUUIDs and the transmission of multiple entryUUIDs in a single syncIdSet message.
At the end of the refreshOnly synchronization, the provider sends a synchronization cookie to the consumer as a state indicator of the consumer copy after the synchronization is completed. The consumer will present the received cookie when it requests the next incremental synchronization to the provider.
When refreshAndPersist synchronization is used, the provider sends a synchronization cookie at the end of the refresh stage by sending a Sync Info message with refreshDone=TRUE. It also sends a synchronization cookie by attaching it to SearchResultEntry messages generated in the persist stage of the synchronization search. During the persist stage, the provider can also send a Sync Info message containing the synchronization cookie at any time the provider wants to update the consumer-side state indicator.
In the LDAP Sync protocol, entries are uniquely identified by the entryUUID attribute value. It can function as a reliable identifier of the entry. The DN of the entry, on the other hand, can be changed over time and hence cannot be considered as the reliable identifier. The entryUUID is attached to each SearchResultEntry or SearchResultReference as a part of the synchronization control.
Syncrepl细节
The syncrepl engine utilizes both the refreshOnly and the refreshAndPersist operations of the LDAP Sync protocol. If a syncrepl specification is included in a database definition, slapd(8) launches a syncrepl engine as a slapd(8) thread and schedules its execution. If the refreshOnly operation is specified, the syncrepl engine will be rescheduled at the interval time after a synchronization operation is completed. If the refreshAndPersist operation is specified, the engine will remain active and process the persistent synchronization messages from the provider.
The syncrepl engine utilizes both the present phase and the delete phase of the refresh synchronization. It is possible to configure a session log in the provider which stores the entryUUIDs of a finite number of entries deleted from a database. Multiple replicas share the same session log. The syncrepl engine uses the delete phase if the session log is present and the state of the consumer server is recent enough that no session log entries are truncated after the last synchronization of the client. The syncrepl engine uses the present phase if no session log is configured for the replication content or if the consumer replica is too outdated to be covered by the session log. The current design of the session log store is memory based, so the information contained in the session log is not persistent over multiple provider invocations. It is not currently supported to access the session log store by using LDAP operations. It is also not currently supported to impose access control to the session log.
As a further optimization, even in the case the synchronization search is not associated with any session log, no entries will be transmitted to the consumer server when there has been no update in the replication context.
The syncrepl engine, which is a consumer-side replication engine, can work with any backends. The LDAP Sync provider can be configured as an overlay on any backend, but works best with the back-bdb or back-hdb backend.
The LDAP Sync provider maintains a contextCSN for each database as the current synchronization state indicator of the provider content. It is the largest entryCSN in the provider context such that no transactions for an entry having smaller entryCSN value remains outstanding. The contextCSN could not just be set to the largest issued entryCSN because entryCSN is obtained before a transaction starts and transactions are not committed in the issue order.
The provider stores the contextCSN of a context in the contextCSN attribute of the context suffix entry. The attribute is not written to the database after every update operation though; instead it is maintained primarily in memory. At database start time the provider reads the last saved contextCSN into memory and uses the in-memory copy exclusively thereafter. By default, changes to the contextCSN as a result of database updates will not be written to the database until the server is cleanly shut down. A checkpoint facility exists to cause the contextCSN to be written out more frequently if desired.
Note that at startup time, if the provider is unable to read a contextCSN from the suffix entry, it will scan the entire database to determine the value, and this scan may take quite a long time on a large database. When a contextCSN value is read, the database will still be scanned for any entryCSN values greater than it, to make sure the contextCSN value truly reflects the greatest committed entryCSN in the database. On databases which support inequality indexing, setting an eq index on the entryCSN attribute and configuring contextCSN checkpoints will greatly speed up this scanning step.
If no contextCSN can be determined by reading and scanning the database, a new value will be generated. Also, if scanning the database yielded a greater entryCSN than was previously recorded in the suffix entry's contextCSN attribute, a checkpoint will be immediately written with the new value.
The consumer also stores its replica state, which is the provider's contextCSN received as a synchronization cookie, in the contextCSN attribute of the suffix entry. The replica state maintained by a consumer server is used as the synchronization state indicator when it performs subsequent incremental synchronization with the provider server. It is also used as a provider-side synchronization state indicator when it functions as a secondary provider server in a cascading replication configuration. Since the consumer and provider state information are maintained in the same location within their respective databases, any consumer can be promoted to a provider (and vice versa) without any special actions.
Because a general search filter can be used in the syncrepl specification, some entries in the context may be omitted from the synchronization content. The syncrepl engine creates a glue entry to fill in the holes in the replica context if any part of the replica content is subordinate to the holes. The glue entries will not be returned in the search result unless ManageDsaIT control is provided.
Also as a consequence of the search filter used in the syncrepl specification, it is possible for a modification to remove an entry from the replication scope even though the entry has not been deleted on the provider. Logically the entry must be deleted on the consumer but in refreshOnly mode the provider cannot detect and propagate this change without the use of the session log.
For configuration, please see the Syncrepl section.
部署替代
While the LDAP Sync specification only defines a narrow scope for replication, the OpenLDAP implementation is extremely flexible and supports a variety of operating modes to handle other scenarios not explicitly addressed in the spec.
Delta-syncrepl复制
- LDAP同步复制的缺点:
LDAP同步复制是一个基于对象的复制机制. 当提供者的一个被复制对象中的任何属性值改变时, 每个消费者在复制过程中撷取并处理完整的变更对象, 包括所有改变和没改变的属性值. 这方法的一个好处是当多个变更发生在单一对象上时, 那些变更的精确顺序不需要保存; 只有最终状态是有意义的. 但是当使用模式(匹配的方式)在一次变更中处理很多对象时，这个方法可能有缺点。
例如, 假设你有一个数据库包含 100,000 对象，每个对象是 1 KB . 进一步, 假设你经常运行一个批处理工作来变更主服务器上的 100,000 对象的每一个对象中的一个两字节的属性值. 不算LDAP和TCP/IP协议的开销, 每次你运行这个工作每个消费者将传送并处理 1 GB 的数据，只是为了处理这个 200KB 的变更!
在类似这样的案例中，99.98% 被传送和处理的数据将是多余的, 因为它们代表那些未变更的值. 这是一个对宝贵的传输和处理带宽的浪费并且可能导致发展出不可接受的复制日志的积压. 虽然这个情形是一个极端, 但它有助于演示某些LDAP部署的一个非常真实的问题.
- 看看Delta-syncrepl怎么处理:
Delta-syncrepl, 一个基于变更日志syncrepl变种, 被设计用来处理类似上面所说的情况. Delta-syncrepl通过在提供者一端维护一个可选择深度的变更日志来起作用. 复制消费者为它需要的变更检查这个变更日志，只要变更日志包含它需要的变更，消费者就从变更日志撷取这些变更并把它们应用到自己的数据库. 不过，一个复制（译者注：指变更日志里的变更）如果离上一次同步的状态太远(或消费者根本就是空的), 可以用常规的syncrepl把它（指消费者）恢复到最新的状态然后复制重新切换到delta-syncrepl模式.
关于配置请参考 Delta-syncrepl 章节.
N-Way Multi-Master复制
Multi-Master复制是一个使用Syncrepl复制数据到多个提供者（“主服务器”）目录服务器的复制技术.
对于Multi-Master replication有效的观点
- 如果任何提供者失败了, 其他提供者将继续接受更新
- 避免了单点失败
- 提供者们可以在不同的物理位置例如跨越全球网络.
- 好的自动容错/高可用性
对于Multi-Master replication无效的观点
(这些经常被声称是Multi-Master复制的优点但是那些说法是错误的):
- 它不关负载均衡任何事
- 提供者必须对所有其他的服务器进行写操作，这意味着分布在所有的服务器上的网络交通和写操作负载,和单一主服务器是一样的。
- 多服务器的服务器利用率和负载在最好的情况下和单服务器一样; 最坏的情况下单服务器更优，因为在提供者和消费者之间使用不同的模式的时候索引可以做出不同的优化调整.
和Multi-Master replication抵触的观点
- 打破了目录模式的数据一致性的保障
- http://www.openldap.org/faq/data/cache/1240.html
- 如果提供者的连接因为网络问题丢失了, 那么 "自动容错" 只会使问题复杂化
- 通常, 一个特定的机器不能区分失去和一个节点的联系是因为该节点崩溃了还是因为网络连接失败了a
- 如果一个网络是分割开的而多个客户端开始向每一个"主服务器"写操作，那么和解将是一个痛苦; 可能最好的办法是禁止那些被单一提供者分隔开的客户端的写操作
关于配置，请看下面的 N-Way Multi-Master 章节
MirrorMode复制
MirrorMode是一个混合配置，既提供单主服务器复制的所有一致性保障，也提供多主服务器模式的高可用性. 在 MirrorMode 两个提供者都被设置成从对方复制(就象一个多主服务器配置), 但是一个额外的前段被用来引导所有的写操作到仅仅到两台服务器中的其中一台. 第二个提供者将只在第一台服务器崩溃时进行写操作, 那时这个前端将切换路径引导所有的写操作到第二个提供者. 当一个崩溃的提供者被修复并且重启动后将自动从正在运行的提供者那里活得任何更新并重新同步.
MirrorMode的观点
- 对于目录的写操作提供了一个高可用性 (HA) 方案(复制处理读操作)
- 只有一个提供者是可操作的l, 写操作的安全是可接受的
- 提供者节点从对方互相复制, 所以它们总是最新的并且可以随时准备好接管 (热备份)
- Syncrepl也允许提供者节点在任何停机时间进行重新同步
和MirrorMode抵触的观点
- MirrorMode 不能被称为多主机方案. 这是因为同一时间写操作不得不仅限于镜像节点中的一个
- MirrorMode 可被称为Active-Active Hot-Standby（“双活热备份”,呃，这个翻译怎么样，传神不？）, 因此需要一个额外的服务器(代理模式的slapd)或设备(硬件负载平衡装置)来管理哪个提供者是当前激活的
- 备份的管理稍微不同
- 如果备份bdb本身并且定期备份事务日志文件，那么镜像对的相同数字需要用于收集日志文件直到下一次数据库备份发生
- 为了确保所有数据库都是一致的, 当执行一个slapcat的时候每个数据库可能都不得不置于只读模式.
- Delta-Syncrepl扔不支持
关于配置，请看下面的 MirrorMode 章节
Syncrepl代理模式
因为LDAP同步协议同时支持基于“拉”和“推”的复制, “推”模式 (refreshAndPersist) 在提供者开始"推"变更之前仍必须由消费者初始化. 在一些网络配置中, 特别是防火墙限制了连接的方向时, 一个提供者初始化的推模式是需要的.
这个模式可以被配置成LDAP Backend (Backends and slapd-ldap(8)). 不用在实际的消费者服务器上运行syncrepl引擎, 而是一个slapd-ldap代理设置在靠近（或搭配在）提供者的地方指向消费者, 而这个syncrepl引擎运行在这个代理服务器上.
关于配置, 请看 Syncrepl代理 章节.
替代Slurpd
旧的slurpd机制只操作主服务器初始化的推模式. Slurpd复制被Syncrepl复制取代了并且在OpenLDAP 2.4中被完全移除了.
slurpd守护进程是原来继承自UMich's LDAP的复制机制并且以推模式操作: 主服务器推变更到从服务器. 因为多种原因它被替换掉, 简短的说:
- 它是不可靠的
- 它对replog中的记录的次序极为敏感
- 它可能很容易失去同步, 这时需要手工干预来从主目录重新同步从服务器数据库
- 它对不可用的服务器不是非常宽容. 如果一个从服务器长时间停机, replog可能变得太大以至于slurpd无法处理
- 它只工作在推模式
- 它需要停止和重新启动主服务器来增加从服务器
- 它只支持单一主服务器复制
- 它是不可靠的
Syncrepl没有那些弱点:
- Syncrepl是自同步的; 你可以在任何状态启动一个消费者数据库，从完全空的到完全同步的，它将自动做正确的事来完成和维护同步
- 它对变更发生的次序完全不敏感
- 它保障消费者和提供者内容的合流,不用手工干预
- 无论一个消费者多长时间没有联系提供者，它都能重新同步
- Syncrepl能双向操作
- 消费者能在不用碰提供者的情况下被加入
- 支持多主服务器复制
- Syncrepl是自同步的; 你可以在任何状态启动一个消费者数据库，从完全空的到完全同步的，它将自动做正确的事来完成和维护同步
配置不同的复制类型
Syncrepl
Syncrepl配置
因为syncrepl是一个消费方的复制引擎, syncrepl规范定义在 slapd.conf(5) 的消费者服务器, 而不是在提供者的服务器配置文件里. 复制内容的初始化装载可以有两种执行方式，以无同步cookie的方式启动一个syncrepl 引擎，或装载一个提供者服务器的全备份LDIF文件填充到消费者服务器.
当从一个备份装载的时候, 它不需要执行从提供者内容的最新备份初始化装载这个动作. syncrepl引擎将自动同步初始化的消费者复制当前的提供者内容. 结果是, 它不需要为了避免由于内容备份和装载过程中提供者服务器仍在更新而导致复制不一致的问题来停止提供者服务器.
当复制一个大规模的目录时, 特别是在一个带宽受限的环境, 建议从备份装载消费者而不是使用syncrepl执行一个完全的初始化装载.
设置提供者的slapd
The provider is implemented as an overlay, so the overlay itself must first be configured in slapd.conf(5) before it can be used. The provider has only two configuration directives, for setting checkpoints on the contextCSN and for configuring the session log. Because the LDAP Sync search is subject to access control, proper access control privileges should be set up for the replicated content.
The contextCSN checkpoint is configured by the
syncprov-checkpoint <ops> <minutes>
directive. Checkpoints are only tested after successful write operations. If <ops> operations or more than <minutes> time has passed since the last checkpoint, a new checkpoint is performed.
The session log is configured by the
syncprov-sessionlog <size>
directive, where <size> is the maximum number of session log entries the session log can record. When a session log is configured, it is automatically used for all LDAP Sync searches within the database.
Note that using the session log requires searching on the entryUUID attribute. Setting an eq index on this attribute will greatly benefit the performance of the session log on the provider.
A more complete example of the slapd.conf(5) content is thus:
database bdb
suffix dc=Example,dc=com
rootdn dc=Example,dc=com
directory /var/ldap/db
index objectclass,entryCSN,entryUUID eq
overlay syncprov
syncprov-checkpoint 100 10
syncprov-sessionlog 100
设置消费者的slapd
The syncrepl replication is specified in the database section of slapd.conf(5) for the replica context. The syncrepl engine is backend independent and the directive can be defined with any database type.
database hdb
suffix dc=Example,dc=com
rootdn dc=Example,dc=com
directory /var/ldap/db
index objectclass,entryCSN,entryUUID eq
syncrepl rid=123
provider=ldap://provider.example.com:389
type=refreshOnly
interval=01:00:00:00
searchbase="dc=example,dc=com"
filter="(objectClass=organizationalPerson)"
scope=sub
attrs="cn,sn,ou,telephoneNumber,title,l"
schemachecking=off
bindmethod=simple
binddn="cn=syncuser,dc=example,dc=com"
credentials=secret
In this example, the consumer will connect to the provider slapd(8) at port 389 of ldap://provider.example.com to perform a polling (refreshOnly) mode of synchronization once a day. It will bind as cn=syncuser,dc=example,dc=com using simple authentication with password "secret". Note that the access control privilege of cn=syncuser,dc=example,dc=com should be set appropriately in the provider to retrieve the desired replication content. Also the search limits must be high enough on the provider to allow the syncuser to retrieve a complete copy of the requested content. The consumer uses the rootdn to write to its database so it always has full permissions to write all content.
The synchronization search in the above example will search for the entries whose objectClass is organizationalPerson in the entire subtree rooted at dc=example,dc=com. The requested attributes are cn, sn, ou, telephoneNumber, title, and l. The schema checking is turned off, so that the consumer slapd(8) will not enforce entry schema checking when it processes updates from the provider slapd(8).
For more detailed information on the syncrepl directive, see the syncrepl section of The slapd Configuration File chapter of this admin guide.
启动提供者和消费者的slapd
The provider slapd(8) is not required to be restarted. contextCSN is automatically generated as needed: it might be originally contained in the LDIF file, generated by slapadd (8), generated upon changes in the context, or generated when the first LDAP Sync search arrives at the provider. If an LDIF file is being loaded which did not previously contain the contextCSN, the -w option should be used with slapadd (8) to cause it to be generated. This will allow the server to startup a little quicker the first time it runs.
When starting a consumer slapd(8), it is possible to provide a synchronization cookie as the -c cookie command line option in order to start the synchronization from a specific state. The cookie is a comma separated list of name=value pairs. Currently supported syncrepl cookie fields are csn=<csn> and rid=<rid>. <csn> represents the current synchronization state of the consumer replica. <rid> identifies a consumer replica locally within the consumer server. It is used to relate the cookie to the syncrepl definition in slapd.conf(5) which has the matching replica identifier. The <rid> must have no more than 3 decimal digits. The command line cookie overrides the synchronization cookie stored in the consumer replica database.
Delta-syncrepl
Delta-syncrepl提供者配置
Setting up delta-syncrepl requires configuration changes on both the master and replica servers:
# Give the replica DN unlimited read access. This ACL needs to be
# merged with other ACL statements, and/or moved within the scope
# of a database. The "by * break" portion causes evaluation of
# subsequent rules. See slapd.access(5) for details.
access to *
by dn.base="cn=replicator,dc=symas,dc=com" read
by * break
# Set the module path location
modulepath /opt/symas/lib/openldap
# Load the hdb backend
moduleload back_hdb.la
# Load the accesslog overlay
moduleload accesslog.la
#Load the syncprov overlay
moduleload syncprov.la
# Accesslog database definitions
database hdb
suffix cn=accesslog
directory /db/accesslog
rootdn cn=accesslog
index default eq
index entryCSN,objectClass,reqEnd,reqResult,reqStart
overlay syncprov
syncprov-nopresent TRUE
syncprov-reloadhint TRUE
# Let the replica DN have limitless searches
limits dn.exact="cn=replicator,dc=symas,dc=com" time.soft=unlimited time.hard=unlimited size.soft=unlimited size.hard=unlimited
# Primary database definitions
database hdb
suffix "dc=symas,dc=com"
rootdn "cn=manager,dc=symas,dc=com"
## Whatever other configuration options are desired
# syncprov specific indexing
index entryCSN eq
index entryUUID eq
# syncrepl Provider for primary db
overlay syncprov
syncprov-checkpoint 1000 60
# accesslog overlay definitions for primary db
overlay accesslog
logdb cn=accesslog
logops writes
logsuccess TRUE
# scan the accesslog DB every day, and purge entries older than 7 days
logpurge 07+00:00 01+00:00
# Let the replica DN have limitless searches
limits dn.exact="cn=replicator,dc=symas,dc=com" time.soft=unlimited time.hard=unlimited size.soft=unlimited size.hard=unlimited
For more information, always consult the relevant man pages (slapo-accesslog(5) and slapd.conf(5))
Delta-syncrepl消费者配置
# Replica database configuration
database hdb
suffix "dc=symas,dc=com"
rootdn "cn=manager,dc=symas,dc=com"
## Whatever other configuration bits for the replica, like indexing
## that you want
# syncrepl specific indices
index entryUUID eq
# syncrepl directives
syncrepl rid=0
provider=ldap://ldapmaster.symas.com:389
bindmethod=simple
binddn="cn=replicator,dc=symas,dc=com"
credentials=secret
searchbase="dc=symas,dc=com"
logbase="cn=accesslog"
logfilter="(&(objectClass=auditWriteObject)(reqResult=0))"
schemachecking=on
type=refreshAndPersist
retry="60 +"
syncdata=accesslog
# Refer updates to the master
updateref ldap://ldapmaster.symas.com
The above configuration assumes that you have a replicator identity defined in your database that can be used to bind to the provider. In addition, all of the databases (primary, replica, and the accesslog storage database) should also have properly tuned DB_CONFIG files that meet your needs.
N-Way Multi-Master
For the following example we will be using 3 Master nodes. Keeping in line with test050-syncrepl-multimaster of the OpenLDAP test suite, we will be configuring slapd(8) via cn=config
This sets up the config database:
dn: cn=config
objectClass: olcGlobal
cn: config
olcServerID: 1
dn: olcDatabase={0}config,cn=config
objectClass: olcDatabaseConfig
olcDatabase: {0}config
olcRootPW: secret
second and third servers will have a different olcServerID obviously:
dn: cn=config
objectClass: olcGlobal
cn: config
olcServerID: 2
dn: olcDatabase={0}config,cn=config
objectClass: olcDatabaseConfig
olcDatabase: {0}config
olcRootPW: secret
This sets up syncrepl as a provider (since these are all masters):
dn: cn=module,cn=config
objectClass: olcModuleList
cn: module
olcModulePath: /usr/local/libexec/openldap
olcModuleLoad: syncprov.la
Now we setup the first Master Node (replace $URI1, $URI2 and $URI3 etc. with your actual ldap urls):
dn: cn=config
changetype: modify
replace: olcServerID
olcServerID: 1 $URI1
olcServerID: 2 $URI2
olcServerID: 3 $URI3
dn: olcOverlay=syncprov,olcDatabase={0}config,cn=config
changetype: add
objectClass: olcOverlayConfig
objectClass: olcSyncProvConfig
olcOverlay: syncprov
dn: olcDatabase={0}config,cn=config
changetype: modify
add: olcSyncRepl
olcSyncRepl: rid=001 provider=$URI1 binddn="cn=config" bindmethod=simple
credentials=secret searchbase="cn=config" type=refreshAndPersist
retry="5 5 300 5" timeout=1
olcSyncRepl: rid=002 provider=$URI2 binddn="cn=config" bindmethod=simple
credentials=secret searchbase="cn=config" type=refreshAndPersist
retry="5 5 300 5" timeout=1
olcSyncRepl: rid=003 provider=$URI3 binddn="cn=config" bindmethod=simple
credentials=secret searchbase="cn=config" type=refreshAndPersist
retry="5 5 300 5" timeout=1
-
add: olcMirrorMode
olcMirrorMode: TRUE
Now start up the Master and a consumer/s, also add the above LDIF to the first consumer, second consumer etc. It will then replicate cn=config. You now have N-Way Multimaster on the config database.
We still have to replicate the actual data, not just the config, so add to the master (all active and configured consumers/masters will pull down this config, as they are all syncing). Also, replace all ${} variables with whatever is applicable to your setup:
dn: olcDatabase={1}$BACKEND,cn=config
objectClass: olcDatabaseConfig
objectClass: olc${BACKEND}Config
olcDatabase: {1}$BACKEND
olcSuffix: $BASEDN
olcDbDirectory: ./db
olcRootDN: $MANAGERDN
olcRootPW: $PASSWD
olcLimits: dn.exact="$MANAGERDN" time.soft=unlimited time.hard=unlimited size.soft=unlimited size.hard=unlimited
olcSyncRepl: rid=004 provider=$URI1 binddn="$MANAGERDN" bindmethod=simple
credentials=$PASSWD searchbase="$BASEDN" type=refreshOnly
interval=00:00:00:10 retry="5 5 300 5" timeout=1
olcSyncRepl: rid=005 provider=$URI2 binddn="$MANAGERDN" bindmethod=simple
credentials=$PASSWD searchbase="$BASEDN" type=refreshOnly
interval=00:00:00:10 retry="5 5 300 5" timeout=1
olcSyncRepl: rid=006 provider=$URI3 binddn="$MANAGERDN" bindmethod=simple
credentials=$PASSWD searchbase="$BASEDN" type=refreshOnly
interval=00:00:00:10 retry="5 5 300 5" timeout=1
olcMirrorMode: TRUE
dn: olcOverlay=syncprov,olcDatabase={1}${BACKEND},cn=config
changetype: add
objectClass: olcOverlayConfig
objectClass: olcSyncProvConfig
olcOverlay: syncprov
Note: All of your servers' clocks must be tightly synchronized using e.g. NTP http://www.ntp.org/, atomic clock, or some other reliable time reference.
Note: As stated in slapd-config(5), URLs specified in olcSyncRepl directives are the URLs of the servers from which to replicate. These must exactly match the URLs slapd listens on (-h in Command-Line Options). Otherwise slapd may attempt to replicate from itself, causing a loop.
MirrorMode
MirrorMode configuration is actually very easy. If you have ever setup a normal slapd syncrepl provider, then the only change is the following two directives:
mirrormode on
serverID 1
Note: You need to make sure that the serverID of each mirror node is different and add it as a global configuration option.
Mirror Node配置
The first step is to configure the syncrepl provider the same as in the Set up the provider slapd section.
Note: Delta-syncrepl is not yet supported with MirrorMode.
Here's a specific cut down example using LDAP Sync Replication in refreshAndPersist mode:
MirrorMode node 1:
# Global section
serverID 1
# database section
# syncrepl directive
syncrepl rid=001
provider=ldap://ldap-sid2.example.com
bindmethod=simple
binddn="cn=mirrormode,dc=example,dc=com"
credentials=mirrormode
searchbase="dc=example,dc=com"
schemachecking=on
type=refreshAndPersist
retry="60 +"
mirrormode on
MirrorMode node 2:
# Global section
serverID 2
# database section
# syncrepl directive
syncrepl rid=001
provider=ldap://ldap-sid1.example.com
bindmethod=simple
binddn="cn=mirrormode,dc=example,dc=com"
credentials=mirrormode
searchbase="dc=example,dc=com"
schemachecking=on
type=refreshAndPersist
retry="60 +"
mirrormode on
It's simple really; each MirrorMode node is setup exactly the same, except that the serverID is unique, and each consumer is pointed to the other server.
容错配置
There are generally 2 choices for this; 1. Hardware proxies/load-balancing or dedicated proxy software, 2. using a Back-LDAP proxy as a syncrepl provider
A typical enterprise example might be:
Figure X.Y: MirrorMode in a Dual Data Center Configuration
标准消费者配置
This is exactly the same as the Set up the consumer slapd section. It can either setup in normal syncrepl replication mode, or in delta-syncrepl replication mode.
MirrorMode总结
You will now have a directory architecture that provides all of the consistency guarantees of single-master replication, while also providing the high availability of multi-master replication.
Syncrepl代理
Figure X.Y: Replacing slurpd
The following example is for a self-contained push-based replication solution:
#######################################################################
# Standard OpenLDAP Master/Provider
#######################################################################
include /usr/local/etc/openldap/schema/core.schema
include /usr/local/etc/openldap/schema/cosine.schema
include /usr/local/etc/openldap/schema/nis.schema
include /usr/local/etc/openldap/schema/inetorgperson.schema
include /usr/local/etc/openldap/slapd.acl
modulepath /usr/local/libexec/openldap
moduleload back_hdb.la
moduleload syncprov.la
moduleload back_monitor.la
moduleload back_ldap.la
pidfile /usr/local/var/slapd.pid
argsfile /usr/local/var/slapd.args
loglevel sync stats
database hdb
suffix "dc=suretecsystems,dc=com"
directory /usr/local/var/openldap-data
checkpoint 1024 5
cachesize 10000
idlcachesize 10000
index objectClass eq
# rest of indexes
index default sub
rootdn "cn=admin,dc=suretecsystems,dc=com"
rootpw testing
# syncprov specific indexing
index entryCSN eq
index entryUUID eq
# syncrepl Provider for primary db
overlay syncprov
syncprov-checkpoint 1000 60
# Let the replica DN have limitless searches
limits dn.exact="cn=replicator,dc=suretecsystems,dc=com" time.soft=unlimited time.hard=unlimited size.soft=unlimited size.hard=unlimited
database monitor
database config
rootpw testing
##############################################################################
# Consumer Proxy that pulls in data via Syncrepl and pushes out via slapd-ldap
##############################################################################
database ldap
# ignore conflicts with other databases, as we need to push out to same suffix
hidden on
suffix "dc=suretecsystems,dc=com"
rootdn "cn=slapd-ldap"
uri ldap://localhost:9012/
lastmod on
# We don't need any access to this DSA
restrict all
acl-bind bindmethod=simple
binddn="cn=replicator,dc=suretecsystems,dc=com"
credentials=testing
syncrepl rid=001
provider=ldap://localhost:9011/
binddn="cn=replicator,dc=suretecsystems,dc=com"
bindmethod=simple
credentials=testing
searchbase="dc=suretecsystems,dc=com"
type=refreshAndPersist
retry="5 5 300 5"
overlay syncprov
A replica configuration for this type of setup could be:
#######################################################################
# Standard OpenLDAP Slave without Syncrepl
#######################################################################
include /usr/local/etc/openldap/schema/core.schema
include /usr/local/etc/openldap/schema/cosine.schema
include /usr/local/etc/openldap/schema/nis.schema
include /usr/local/etc/openldap/schema/inetorgperson.schema
include /usr/local/etc/openldap/slapd.acl
modulepath /usr/local/libexec/openldap
moduleload back_hdb.la
moduleload syncprov.la
moduleload back_monitor.la
moduleload back_ldap.la
pidfile /usr/local/var/slapd.pid
argsfile /usr/local/var/slapd.args
loglevel sync stats
database hdb
suffix "dc=suretecsystems,dc=com"
directory /usr/local/var/openldap-slave/data
checkpoint 1024 5
cachesize 10000
idlcachesize 10000
index objectClass eq
# rest of indexes
index default sub
rootdn "cn=admin,dc=suretecsystems,dc=com"
rootpw testing
# Let the replica DN have limitless searches
limits dn.exact="cn=replicator,dc=suretecsystems,dc=com" time.soft=unlimited time.hard=unlimited size.soft=unlimited size.hard=unlimited
updatedn "cn=replicator,dc=suretecsystems,dc=com"
# Refer updates to the master
updateref ldap://localhost:9011
database monitor
database config
rootpw testing
You can see we use the updatedn directive here and example ACLs (usr/local/etc/openldap/slapd.acl) for this could be:
# Give the replica DN unlimited read access. This ACL may need to be
# merged with other ACL statements.
access to *
by dn.base="cn=replicator,dc=suretecsystems,dc=com" write
by * break
access to dn.base=""
by * read
access to dn.base="cn=Subschema"
by * read
access to dn.subtree="cn=Monitor"
by dn.exact="uid=admin,dc=suretecsystems,dc=com" write
by users read
by * none
access to *
by self write
by * read
In order to support more replicas, just add more database ldap sections and increment the syncrepl rid number accordingly.
Note: You must populate the Master and Slave directories with the same data, unlike when using normal Syncrepl
If you do not have access to modify the master directory configuration you can configure a standalone ldap proxy, which might look like:
Figure X.Y: Replacing slurpd with a standalone version
The following configuration is an example of a standalone LDAP Proxy:
include /usr/local/etc/openldap/schema/core.schema
include /usr/local/etc/openldap/schema/cosine.schema
include /usr/local/etc/openldap/schema/nis.schema
include /usr/local/etc/openldap/schema/inetorgperson.schema
include /usr/local/etc/openldap/slapd.acl
modulepath /usr/local/libexec/openldap
moduleload syncprov.la
moduleload back_ldap.la
##############################################################################
# Consumer Proxy that pulls in data via Syncrepl and pushes out via slapd-ldap
##############################################################################
database ldap
# ignore conflicts with other databases, as we need to push out to same suffix
hidden on
suffix "dc=suretecsystems,dc=com"
rootdn "cn=slapd-ldap"
uri ldap://localhost:9012/
lastmod on
# We don't need any access to this DSA
restrict all
acl-bind bindmethod=simple
binddn="cn=replicator,dc=suretecsystems,dc=com"
credentials=testing
syncrepl rid=001
provider=ldap://localhost:9011/
binddn="cn=replicator,dc=suretecsystems,dc=com"
bindmethod=simple
credentials=testing
searchbase="dc=suretecsystems,dc=com"
type=refreshAndPersist
retry="5 5 300 5"
overlay syncprov
As you can see, you can let your imagination go wild using Syncrepl and slapd-ldap(8) tailoring your replication to fit your specific network topology.
