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website: getting started registeringa service changes

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Mitchell Hashimoto 2014-04-14 12:38:24 -07:00
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137
website/source/intro/getting-started/services.html.markdown
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@ -6,58 +6,72 @@ sidebar_current: "gettingstarted-services"
# Registering Services
In the previous page, we created a simple cluster. Although the cluster members
could see each other, there were no registered services. In this page, we'll
modify our client to export a service.
In the previous page, we ran our first agent, saw the cluster members, and
queried that node. On this page, we'll register our first service and query
that service. We're not yet running a cluster of Consul agents.
## Defining a Service
A service can be registered either by providing a [service definition](/docs/agent/services.html),
or by making the appropriate calls to the [HTTP API](/docs/agent/http.html). First we
start by providing a simple service definition. We will by using the same setup as in the
[last page](/intro/getting-started/join.html). On the second node, we start by creating a
simple configuration:
A service can be registered either by providing a
[service definition](/docs/agent/services.html),
or by making the appropriate calls to the
[HTTP API](/docs/agent/http.html).
We're going to start by registering a service using a service definition,
since this is the most common way that services are registered. We'll be
building on what we covered in the
[previous page](/intro/getting-started/agent.html).
First, create a directory for Consul configurations. A good directory
is typically `/etc/consul.d`. Consul loads all configuration files in the
configuration directory.
```
$ sudo mkdir /etc/consul
$ echo '{"service": {"name": "web", "tags": ["rails"], "port": 80}}' | sudo tee /etc/consul/web.json
$ sudo mkdir /etc/consul.d
```
We now restart the second agent, providing the configuration directory as well as the
first node to re-join:
Next, we'll write a service definition configuration file. We'll
pretend we have a service named "web" running on port 80. Additionally,
we'll give it some tags, which we can use as additional ways to query
it later.
```
$ consul agent -data-dir /tmp/consul -node=agent-two -bind=172.20.20.11 -config-dir /etc/consul/
$ echo '{"service": {"name": "web", "tags": ["rails"], "port": 80}}' \
>/etc/consul.d/web.json
```
Now, restart the agent we're running, providing the configuration directory:
```
$ consul agent -server -bootstrap -data-dir /tmp/consul -config-dir /etc/consul.d
==> Starting Consul agent...
...
[INFO] agent: Synced service 'web'
...
```
You'll notice in the output that it "synced" the web service. This means
that it loaded the information from the configuration.
If you wanted to register multiple services, you create multiple service
definition files in the Consul configuration directory.
## Querying Services
Once the agent gets started, we should see a log output indicating that the `web` service
has been synced with the Consul servers. We can first check using the HTTP API:
Once the agent is started and the service is synced, we can query that
service using either the DNS or HTTP API.
```
$ curl http://localhost:8500/v1/catalog/service/web
[{"Node":"agent-two","Address":"172.20.20.11","ServiceID":"web","ServiceName":"web","ServiceTags":["rails"],"ServicePort":80}]
```
### DNS API
We can also do a simple DNS lookup for any nodes providing the `web` service:
Let's first query it using the DNS API. For the DNS API, the DNS name
for services is `NAME.service.consul`. All DNS names are always in the
`consul` namespace. The `service` subdomain on that tells Consul we're
querying services, and the `NAME` is the name of the service. For the
web service we registered, that would be `web.service.consul`:
```
$ dig @127.0.0.1 -p 8600 web.service.consul
; <<>> DiG 9.8.1-P1 <<>> @127.0.0.1 -p 8600 web.service.consul
; (1 server found)
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 1204
;; flags: qr aa rd; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 0
;; WARNING: recursion requested but not available
...
;; QUESTION SECTION:
;web.service.consul. IN A
@ -66,31 +80,60 @@ $ dig @127.0.0.1 -p 8600 web.service.consul
web.service.consul. 0 IN A 172.20.20.11
```
We can also filter on tags, here only requesting services matching the `rails` tag,
and specifically requesting SRV records:
As you can see, an A record was returned with the IP address of the node that
the service is available on. A records can only hold IP addresses. You can
also use the DNS API to retrieve the entire address/port pair using SRV
records:
```
$ dig @127.0.0.1 -p 8600 web.service.consul SRV
...
;; QUESTION SECTION:
;web.service.consul. IN SRV
;; ANSWER SECTION:
web.service.consul. 0 IN SRV 1 1 80 agent-one.node.dc1.consul.
;; ADDITIONAL SECTION:
agent-one.node.dc1.consul. 0 IN A 172.20.20.11
```
The SRV record returned says that the web service is running on port 80
and exists on the node `agent-one.node.dc1.consul.`. An additional section
is returned by the DNS with the A record for that node.
Finally, we can also use the DNS API to filter services by tags. The
format for tag-based service queries is `TAG.NAME.service.consul`. In
the example below, we ask Consul for all web services with the "rails"
tag. We get a response since we registered our service with that tag.
```
$ dig @127.0.0.1 -p 8600 rails.web.service.consul SRV
; <<>> DiG 9.8.1-P1 <<>> @127.0.0.1 -p 8600 rails.web.service.consul SRV
; (1 server found)
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 45798
;; flags: qr aa rd; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 1
;; WARNING: recursion requested but not available
...
;; QUESTION SECTION:
;rails.web.service.consul. IN SRV
;rails.web.service.consul. IN A
;; ANSWER SECTION:
rails.web.service.consul. 0 IN SRV 1 1 80 agent-two.node.dc1.consul.
;; ADDITIONAL SECTION:
agent-two.node.dc1.consul. 0 IN A 172.20.20.11
rails.web.service.consul. 0 IN A 172.20.20.11
```
This shows how simple it is to get started with services. Service definitions
can be updated by changing configuration files and sending a `SIGHUP` to the agent.
Alternatively the HTTP API can be used to add, remove and modify services dynamically.
### HTTP API
In addition to the DNS API, the HTTP API can be used to query services:
```
$ curl http://localhost:8500/v1/catalog/service/web
[{"Node":"agent-one","Address":"172.20.20.11","ServiceID":"web","ServiceName":"web","ServiceTags":["rails"],"ServicePort":80}]
```
## Updating Services
Service definitions can be updated by changing configuration files and
sending a `SIGHUP` to the agent. This lets you update services without
any downtime or unavailability to service queries.
Alternatively the HTTP API can be used to add, remove, and modify services
dynamically.

10
website/source/layouts/intro.erb
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@ -50,17 +50,17 @@
<a href="/intro/getting-started/agent.html">Run the Agent</a>
</li>
<li<%= sidebar_current("gettingstarted-services") %>>
<a href="/intro/getting-started/services.html">Services</a>
</li>
<li<%= sidebar_current("gettingstarted-join") %>>
<a href="/intro/getting-started/join.html">Join a Cluster</a>
</li>
<li<%= sidebar_current("gettingstarted-services") %>>
<a href="/intro/getting-started/services.html">Services</a>
</li>
<li<%= sidebar_current("gettingstarted-checks") %>>
<a href="/intro/getting-started/checks.html">Health Checks</a>
</li>
</li>
<li<%= sidebar_current("gettingstarted-kv") %>>
<a href="/intro/getting-started/kv.html">Key/Value Data</a>