167 lines
5.6 KiB
Plaintext
167 lines
5.6 KiB
Plaintext
---
|
|
layout: intro
|
|
page_title: Registering Services
|
|
description: >
|
|
A service can be registered either by providing a service definition or by
|
|
making the appropriate calls to the HTTP API. A configuration file is the most
|
|
common, so we will use this approach to register a service, and then query
|
|
that service using the REST API and DNS interfaces.
|
|
---
|
|
|
|
# Registering Services
|
|
|
|
In the previous step, we ran our first agent, saw the cluster members (well,
|
|
our cluster _member_), and queried that node. In this guide, we'll register
|
|
our first service and query that service.
|
|
|
|
## Defining a Service
|
|
|
|
A service can be registered either by providing a
|
|
[service definition](/docs/agent/services) or by making the appropriate
|
|
calls to the [HTTP API](/api).
|
|
|
|
A service definition is the most common way to register services, so we'll
|
|
use that approach for this step. We'll be building on the agent configuration
|
|
we covered in the [previous step](/intro/getting-started/agent).
|
|
|
|
First, create a directory for Consul configuration. Consul loads all
|
|
configuration files in the configuration directory, so a common convention
|
|
on Unix systems is to name the directory something like `/etc/consul.d`
|
|
(the `.d` suffix implies "this directory contains a set of configuration
|
|
files").
|
|
|
|
```shell-session
|
|
$ sudo mkdir /etc/consul.d
|
|
```
|
|
|
|
Next, we'll write a service definition configuration file. Let's
|
|
pretend we have a service named "web" running on port 80. Additionally,
|
|
we'll give it a tag we can use as an additional way to query the service:
|
|
|
|
```shell-session
|
|
$ echo '{"service": {"name": "web", "tags": ["rails"], "port": 80}}' \
|
|
| sudo tee /etc/consul.d/web.json
|
|
```
|
|
|
|
Now, restart the agent, providing the configuration directory:
|
|
|
|
```shell-session
|
|
$ consul agent -dev -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 the agent loaded the service definition from the configuration file,
|
|
and has successfully registered it in the service catalog.
|
|
|
|
If you wanted to register multiple services, you could create multiple
|
|
service definition files in the Consul configuration directory.
|
|
|
|
## Querying Services
|
|
|
|
Once the agent is started and the service is synced, we can query the
|
|
service using either the DNS or HTTP API.
|
|
|
|
### DNS API
|
|
|
|
Let's first query our service using the DNS API. For the DNS API, the
|
|
DNS name for services is `NAME.service.consul`. By default, all DNS names
|
|
are always in the `consul` namespace, though
|
|
[this is configurable](/docs/agent/options#domain). The `service`
|
|
subdomain tells Consul we're querying services, and the `NAME` is the name
|
|
of the service.
|
|
|
|
For the web service we registered, these conventions and settings yield a
|
|
fully-qualified domain name of `web.service.consul`:
|
|
|
|
```shell-session
|
|
$ dig @127.0.0.1 -p 8600 web.service.consul
|
|
...
|
|
|
|
;; QUESTION SECTION:
|
|
;web.service.consul. IN A
|
|
|
|
;; ANSWER SECTION:
|
|
web.service.consul. 0 IN A 172.20.20.11
|
|
```
|
|
|
|
As you can see, an `A` record was returned with the IP address of the node on
|
|
which the service is available. `A` records can only hold IP addresses.
|
|
|
|
You can also use the DNS API to retrieve the entire address/port pair as a
|
|
`SRV` record:
|
|
|
|
```shell-session
|
|
$ 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 Armons-MacBook-Air.node.dc1.consul.
|
|
|
|
;; ADDITIONAL SECTION:
|
|
Armons-MacBook-Air.node.dc1.consul. 0 IN A 172.20.20.11
|
|
```
|
|
|
|
The `SRV` record says that the web service is running on port 80 and exists on
|
|
the node `Armons-MacBook-Air.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 successful response since we registered our service with
|
|
that tag:
|
|
|
|
```shell-session
|
|
$ dig @127.0.0.1 -p 8600 rails.web.service.consul
|
|
...
|
|
|
|
;; QUESTION SECTION:
|
|
;rails.web.service.consul. IN A
|
|
|
|
;; ANSWER SECTION:
|
|
rails.web.service.consul. 0 IN A 172.20.20.11
|
|
```
|
|
|
|
### HTTP API
|
|
|
|
In addition to the DNS API, the HTTP API can be used to query services:
|
|
|
|
```shell-session
|
|
$ curl http://localhost:8500/v1/catalog/service/web
|
|
[{"Node":"Armons-MacBook-Air","Address":"172.20.20.11","ServiceID":"web", \
|
|
"ServiceName":"web","ServiceTags":["rails"],"ServicePort":80}]
|
|
```
|
|
|
|
The catalog API gives all nodes hosting a given service. As we will see later
|
|
with [health checks](/intro/getting-started/checks) you'll typically want
|
|
to query just for healthy instances where the checks are passing. This is what
|
|
DNS is doing under the hood. Here's a query to look for only healthy instances:
|
|
|
|
```shell-session
|
|
$ curl 'http://localhost:8500/v1/health/service/web?passing'
|
|
[{"Node":"Armons-MacBook-Air","Address":"172.20.20.11","Service":{ \
|
|
"ID":"web", "Service":"web", "Tags":["rails"],"Port":80}, "Checks": ...}]
|
|
```
|
|
|
|
## 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.
|
|
|
|
## Next Steps
|
|
|
|
We've now configured a single agent and registered a service. This is good
|
|
progress, but let's explore the full value of Consul by learning how to
|
|
[automatically encrypt and authorize service-to service communication](/intro/getting-started/connect) with Consul Connect.
|