Improve Redis doc for 2.x to avoid common pitfalls #418

andrerom · 2018-10-09T18:59:20Z

Question	Answer
JIRA Ticket
Versions	2.x + master

Updates / Appends Redis doc across Session, Clustering, persistence cache, performance and troubleshooting doc, to try to cover some issues Partners and Community members have been running into over the last few months.

Todo:

Also update and add links on https://doc.ezplatform.com/en/2.3/guide/performance/#redis
...

kmadejski · 2018-10-19T14:06:14Z

docs/getting_started/troubleshooting.md

+
+## Redis: Session are removed or new sessions are refused
+
+See info on [Redis in session doc](../guide/session.md); Ideally use an unique instance of Redis for sessions, that either never runs of of memory or uses an eviction policy that suites your needs.


separated instance perhaps? Sounds more natural for me.

Nitpics:
an unique -> a unique
runs of of memory -> run out of memory
suites -> suits

kmadejski · 2018-10-19T14:11:55Z

docs/guide/persistence_cache.md

@@ -31,8 +20,8 @@ Notes:

 - `UrlWildCardHandler` is not currently cached
 - Currently in case of transactions this is handled very simply by clearing all cache on rollback, this can be improved in the future if needed.
- Some tree/batch operations will cause clearing all persistence cache, this will be improved in the future when we change to a cache service cable of cache tagging.
- Search is not defined as Persistence and the queries themselves are not planned to be cached. Use [Solr](solr.md) which does this for you to improve scale and offload your database.
+- [Cache tagging](https://symfony.com/doc/current/components/cache/cache_invalidation.html#using-cache-tags) is used in order to allow clearing cache by alternative indexes, for instance tree operations or changes to content types are examples of operations that also needs to invalidate content cache by tags.


Nitpic:

needs -> need

kmadejski · 2018-10-19T14:13:52Z

docs/guide/persistence_cache.md

@@ -70,7 +59,7 @@ ezpublish:
        # "site_group" refers to the group configured in site access
        site_group:
            # cache_pool is set to '%env(CACHE_POOL)%'
-            # env(CACHE_POOL) is set to 'cache.app'
+            # env(CACHE_POOL) is set to 'cache.app', a symfony service


Great that you mentioned it, it's not obvious for everyone 👍

WDYT about a symfony service -> a Symfony service, for examples see app/config/cache_pool/*

kmadejski · 2018-10-19T14:19:59Z

docs/guide/persistence_cache.md

@@ -108,7 +97,23 @@ services:

 ##### Redis Cluster

-It is possible to set up and use Redis as a cluster. This configuration is more efficient and reliable for large installations. Redis Cluster can be configured in two ways, the first using [create-cluster script](https://redis.io/topics/cluster-tutorial) and the second using [Redis Sentinel](https://redis.io/topics/sentinel). If you use Platform.sh Enterprise you can benefit from the Redis Sentinel across three nodes for greater fault tolerance. Platform.sh Professional and lower versions offer Redis in single instance mode only. Configuration on eZ Platform / Symfony stays the same regardless of the Redis version, single instance mode or cluster mode.
+Configuration of several Redis instances can be done in several ways, as Persistence cache depends on all involved web servers seeing the same view of the cache as it's shared, the following applies:


Nitpick:
Configuration -> The configuration

As for me this sentence is a little bit too complicated, WDYT about putting it like this:

Configuration of several Redis instances can be done in several ways. Persistence cache depends on all involved web servers, each of them seeing the same view of the cache because it's shared among them. The following configurations are possible:

kmadejski · 2018-10-19T14:20:45Z

docs/guide/persistence_cache.md

-It is possible to set up and use Redis as a cluster. This configuration is more efficient and reliable for large installations. Redis Cluster can be configured in two ways, the first using [create-cluster script](https://redis.io/topics/cluster-tutorial) and the second using [Redis Sentinel](https://redis.io/topics/sentinel). If you use Platform.sh Enterprise you can benefit from the Redis Sentinel across three nodes for greater fault tolerance. Platform.sh Professional and lower versions offer Redis in single instance mode only. Configuration on eZ Platform / Symfony stays the same regardless of the Redis version, single instance mode or cluster mode.
+Configuration of several Redis instances can be done in several ways, as Persistence cache depends on all involved web servers seeing the same view of the cache as it's shared, the following applies:
+- [Redis Cluster](https://redis.io/topics/cluster-tutorial)
+  - Shards cache across several instances in order to be able to cache more then memory of one server allows


Nitpick:

then -> than a

kmadejski · 2018-10-19T14:26:23Z

docs/guide/sessions.md

+        # But in order to use %ezplatform.session.save_path%, default eZ Platform instead sets %ezplatform.session.handler_id% to:
+        # - session.handler.native_file (default)
+        # - ezplatform.core.session.handler.native_redis (recommended value for Cluster usage, using php-redis session handler )
+        handler_id: '%ezplatform.session.handler_id%'


Great to see that in the docs 👍

kmadejski · 2018-10-19T14:27:03Z

docs/guide/sessions.md

-For a [cluster](clustering.md) setup you need to configure sessions to use a back end that is shared between web servers and supports locking.
-The only options out of the box supporting this in Symfony are the native PHP Memcached session save handler
-provided by the `php-memcached` extension, and Symfony session handler for PDO (database).
+For a [cluster](clustering.md) setup you need to configure sessions to use a back end that is shared between web servers.


Nitpick:

back end -> backend (?)

kmadejski · 2018-10-19T14:28:05Z

docs/guide/sessions.md

+##### Storing sessions in Redis using `php-redis`
+
+To set up eZ Platform using the [Redis](https://pecl.php.net/package/redis)
+you need to [configure the session save handler settings in `php.ini`](https://github.com/phpredis/phpredis#php-session-handler),


As far as I know, it's enough to configure it only on eZ (Symfony) side without touching php.ini configuration.

Right, but if they need to configure anything which falls outside the save path DSN, they do need to configure php.ini right? /cc @vidarl

You have an example here https://labs.madisoft.it/scaling-symfony-sessions-with-redis/ So yes you need to provide a DSN
Configuring php.ini means that all your PHP project will use redis. It might not be something you want to do if you share many project on the same server. (or use php_value on vhost by example)

Yeah updated PR text show both ways now, both the way of using what php provides, and the way of using own handler. Both on memcached and redis. And on redis it's what we do by default on platform.sh.

kmadejski · 2018-10-19T14:28:45Z

docs/guide/sessions.md

+and set and set eZ Platform's `%ezplatform.session.handler_id%` to `ezplatform.core.session.handler.native_redis`.
+
+Furthermore when using Redis for sessions make sure to:
+- Either use load balancer with session afiinity, or only Read/write to one Redis instance at a time. _See [Redis Cluster with persistance cache](persistence_cache.md) for furhter info_.


Nitpick:

Read/write -> read/write

kmadejski · 2018-10-19T14:29:22Z

docs/guide/sessions.md

+- Ideally keep [persistance cache](persistence_cache.md) and session data seperated:
+  - Sessions can not risk getting [randomly evicted](https://redis.io/topics/lru-cache#eviction-policies) when you run out of memory for cache.
+  - And you can not disable eviction either, as Redis will then start to refuse new entries once full, including new sessions.
+- If you want to make sure sessions survive Redis or Server restarts, consider using persistant Redis instance for Sessions.


Nitpick:

persistant -> persistent

andrerom · 2018-10-30T08:12:50Z

@kmadejski and @dspe PR updated, please have a look to see if it fits your views on this :)

vidarl · 2018-10-30T08:20:37Z

docs/guide/performance.md

+
+- Memcached/Redis can in some cases perform better then filesystem cache even with a single server, as it offers better general performance for operations invalidating cache.
+    - However, pure read performance is slower, especially if the next points is not optimized.
+    - With cache being on different node(s) then web server, make sure to try to tune latency between the two.


"then" => "than" ?

vidarl · 2018-10-30T09:16:46Z

docs/guide/sessions.md


-##### Storing sessions in Redis using pecl package
+To set up eZ Platform using the [Redis](https://pecl.php.net/package/redis)
+you need to set eZ Platform's `%ezplatform.session.handler_id%` to `ezplatform.core.session.handler.native_redis`,


So, this is not completely correct. Unless you are on Platform.sh you also may configure redis using php.ini settings.
On platform.sh however, you must use ezplatform.core.session.handler.native_redis ( as you don't know the redis configuration at commit/build time )

andrerom · 2018-10-30T19:57:02Z

@vidarl / @kmadejski section on configuring redis / memcached is rewritten.

andrerom · 2018-10-31T11:56:14Z

docs/guide/performance.md

- Redis is recommended over filesystem cache even with a single server, as it offers better general performance for operations invalidating cache.
-    - However, pure read performance is slower, especially if the next point is not optimized.
- If you use Redis, make sure to tune it for in-memory cache usage. Its persistence feature is not needed with eZ Platform cache and will severely slow down execution time.
+### Memcached/Redis


doc review note: this moves the header / anchor back to what it was, and afaik still is in 1.13 doc

andrerom added 3 commits October 9, 2018 16:44

Update persistence cache + improve Redis Cluster doc

c73a86c

Improve Session doc in general and for Redis

5509014

Add troubleshooting doc for Redis

da3c8a1

kmadejski reviewed Oct 19, 2018

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DominikaK added the Needs DEV review label Oct 25, 2018

andrerom changed the title ~~[RFC] Improve Redis doc for 2.x to avoid common pitfalls~~ Improve Redis doc for 2.x to avoid common pitfalls Oct 29, 2018

DominikaK added the Needs DOC review label Oct 29, 2018

Fix comments and todos

7c942f7

Add links to sections from performance page

423baed

vidarl requested changes Oct 30, 2018

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vidarl reviewed Oct 30, 2018

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Update performance.md

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andrerom mentioned this pull request Oct 30, 2018

EZP-25972: Clustering guide improvement #428

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Rewrite section on configuring memcached and redis

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kmadejski approved these changes Oct 30, 2018

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vidarl approved these changes Oct 31, 2018

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andrerom removed the Needs DEV review label Oct 31, 2018

andrerom requested a review from DominikaK October 31, 2018 11:54

andrerom commented Oct 31, 2018

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andrerom and others added 4 commits October 31, 2018 12:59

Add link to sessions doc

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Add more info on redis session config

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Update sessions.md

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Proofing

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DominikaK approved these changes Nov 5, 2018

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DominikaK added Ready for MERGE and removed Needs DOC review labels Nov 5, 2018

DominikaK merged commit 2623405 into 2.3 Nov 6, 2018

DominikaK pushed a commit that referenced this pull request Nov 6, 2018

Improve Redis doc for 2.x to avoid common pitfalls (#418)

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DominikaK pushed a commit that referenced this pull request Nov 6, 2018

Improve Redis doc for 2.x to avoid common pitfalls (#418)

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DominikaK mentioned this pull request Nov 6, 2018

EZP-25972: Clustering guide improvement #443

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andrerom deleted the v2_improve_redis_doc branch November 6, 2018 14:00


		## Redis: Session are removed or new sessions are refused

		See info on [Redis in session doc](../guide/session.md); Ideally use an unique instance of Redis for sessions, that either never runs of of memory or uses an eviction policy that suites your needs.

Improve Redis doc for 2.x to avoid common pitfalls #418

Improve Redis doc for 2.x to avoid common pitfalls #418

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