Christopher Schultz wrote:
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Jeffrey,
On 3/10/14, 10:26 AM, Jeffrey Janner wrote:
-----Original Message----- From: Leo Donahue
[mailto:donahu...@gmail.com] Sent: Friday, March 07, 2014 9:44
AM To: users@tomcat.apache.org Subject: The Service Component
Who uses more than one Service in their server.xml and why? I
get that you can have multiple Connectors if you have multiple
Service components but why use multiple connectors?
Are there any docs on the use cases for these features?
Hi Leo, I may be the only person on this list who does this
consistently. I use it as an alternative method of virtual hosting,
i.e. each host gets its own <Service> and related sub-structure.
The real reason? The default host has to be set to something, and
I don't want to maintain some generic host to catch those that come
in. Since I'm running an SaaS environment, really more ASP, a
business requirement is that each host appear to the outside world
as a unique physical host, so two customers don't get the same IP
address. I could add <Alias> tags for the IP address and all know
variations of the hostname, but there's nothing to keep some yahoo
admin at a customer site from configuring a DNS entry on an
internal DNS server with some name I'm not expecting. Therefore,
each <Engine> in each <Service> gets a defaultHost entry pointing
to its one and only <Host> entry.
I'm interested in this use case.
Since you have to maintain a <Connector> for every IP address already,
how is that different from having a single <Connector> with a bunch of
<Alias> elements? How are those different? Or is it that you need
application isolation in the first place, so this is the best way to
do it in a single JVM?
As an added benefit, if I find I need to move a customer from a
shared Tomcat setup to a unique Tomcat, all I need to do is set up
a new blank Tomcat and move the <Service> structure from one Tomcat
to another. Naturally, there's more work needed if I find I need to
give them their own physical server, but that's to be expected. In
general, not counting any hardware setup, I can move a host to
another tomcat instance with < 2 minutes downtime.
Nice.
It is particularly nice to know that it works, and that the <Service> element really
(apparently) corresponds to "something real" at the Tomcat level. So it is apparently not
just an "element of order" allowing to group Connectors with Engine.
Which is contrary to what I imagined, and which I believe definitely answers the original
OP's question (at least the first part).
And I believe it is worth repeating what was already mentioned earlier regarding the
Service/Connector relationship :
Even if you have only one <Service>, you can have multiple <Connector>'s inside it, and
there are plenty of use cases for that.
And if you have multiple <Service>'s, you can also have more than 1 <Connector> per
<Service>, but each <Connector> (even across <Service>'s) will still need its own unique
listening IP address:Port combination.
As to running multiple <Service>'s within the same Tomcat instance, as opposed to running
multiple single-<Service> Tomcat instances : in the multiple-<Service> scenario, they all
share the same JVM, the same Heap, the same Stack etc. So if you bring one "Service"
down, they all go down.
Which is not the case for multiple Tomcat instances.
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