Cross model relation support has been added to the PostgreSQL Charm for Juju, best experienced with Juju 2.3 or later. When clients also support this feature, you can split your deployment across multiple models, even across controllers and clouds. Making a charms.reactive client charm support cross model relations should involve nothing more than rebuilding and publishing it; the PostgreSQL interface has also been updated and knows how to use the new ingress and egress address information and its API is unchanged.
The main reasons for splitting your deployments into multiple models this way are to spread out parts of your deployment to other availability zones or clouds, or when different teams are maintaining different parts of a complex deployment (e.g. connecting developer maintained clients to DBA maintained back ends.
Here is a brief walk through connecting clients to a server across continents. This example is using two AWS regions, but this works just as well with other supported clouds (Azure, GCE, OpenStack, etc.), and between cloud providers.
First, I’m going to bootstrap two completely independent Juju controllers. Most sites will use a single HA Juju Controller for production, with multiple controllers only desirable when there are independent regional teams needing to maintain independent infrastructure.
$ juju bootstrap aws/ap-southeast-1 --constraints="mem=2G cores=1" singapore Creating Juju controller "singapore" on aws/ap-southeast-1 Looking for packaged Juju agent version 2.3.5 for amd64 Launching controller instance(s) on aws/ap-southeast-1... - i-0fae2f267c2a3c0aa (arch=amd64 mem=2G cores=1)ap-southeast-1a" Installing Juju agent on bootstrap instance Fetching Juju GUI 2.12.1 Waiting for address Attempting to connect to 52.77.212.143:22 Attempting to connect to 172.31.12.2:22 Connected to 52.77.212.143 Running machine configuration script... Bootstrap agent now started Contacting Juju controller at 52.77.212.143 to verify accessibility... Bootstrap complete, "singapore" controller now available Controller machines are in the "controller" model Initial model "default" added $ juju bootstrap aws/ap-southeast-2 sydney Creating Juju controller "sydney" on aws/ap-southeast-2 Looking for packaged Juju agent version 2.3.5 for amd64 Launching controller instance(s) on aws/ap-southeast-2... - i-097eedbeaec354996 (arch=amd64 mem=4G cores=2)ap-southeast-2a" Installing Juju agent on bootstrap instance Fetching Juju GUI 2.12.1 Waiting for address Attempting to connect to 172.31.0.23:22 Attempting to connect to 13.211.134.68:22 Connected to 13.211.134.68 Running machine configuration script... Bootstrap agent now started Contacting Juju controller at 13.211.134.68 to verify accessibility... Bootstrap complete, "sydney" controller now available Controller machines are in the "controller" model Initial model "default" added
Next, I’ll create models in each controller. I’ll deploy a PostgreSQL primary and standby server to Singapore, and some clients to Sydney:
$ juju switch singapore sydney (controller) -> singapore:admin/default $ juju add-model server Uploading credential 'aws/admin/aws' to controller Added 'server' model on aws/ap-southeast-1 with credential 'aws' for user 'admin' $ juju deploy cs:postgresql -n 2 Located charm "cs:postgresql-174". Deploying charm "cs:postgresql-174". $ juju switch sydney $ juju add-model client Uploading credential 'aws/admin/aws' to controller Added 'client' model on aws/ap-southeast-2 with credential 'aws' for user 'admin' $ juju deploy cs:~postgresql-charmers/postgresql-client Located charm "cs:~postgresql-charmers/postgresql-client-5". Deploying charm "cs:~postgresql-charmers/postgresql-client-5".
Offer up the client Application, and consume the offer on the server. I’ll discuss shortly why it is this way around, and the service not being offered to the client:
$ juju offer client.postgresql-client:db client-db Application "postgresql-client" endpoints [db] available at "admin/client.client-db" $ juju status Model Controller Cloud/Region Version SLA client sydney aws/ap-southeast-2 2.3.5 unsupported App Version Status Scale Charm Store Rev OS Notes postgresql-client 9.5 blocked 1 postgresql-client jujucharms 5 ubuntu Unit Workload Agent Machine Public address Ports Message postgresql-client/0* blocked idle 0 13.210.156.16 Needs db relation Machine State DNS Inst id Series AZ Message 0 started 13.210.156.16 i-0849fa7953f3fa1b7 xenial ap-southeast-2a running Offer Application Charm Rev Connected Endpoint Interface Role client-db postgresql-client postgresql-client 5 0/0 db pgsql requirer
$ juju switch singapore:admin/server sydney:admin/client -> singapore:admin/server $ juju consume sydney:admin/client.client-db Added sydney:admin/client.client-db as client-db $ juju status Model Controller Cloud/Region Version SLA server singapore aws/ap-southeast-1 2.3.5 unsupported SAAS Status Store URL client-db blocked sydney admin/client.client-db App Version Status Scale Charm Store Rev OS Notes postgresql 9.5.12 active 2 postgresql jujucharms 174 ubuntu Unit Workload Agent Machine Public address Ports Message postgresql/0* active idle 0 13.229.205.17 5432/tcp Live master (9.5.12) postgresql/1 active idle 1 13.250.20.84 5432/tcp Live secondary (9.5.12) Machine State DNS Inst id Series AZ Message 0 started 13.229.205.17 i-0a0ce0ea34e4451da xenial ap-southeast-1a running 1 started 13.250.20.84 i-0c07e2cb0dfd95b69 xenial ap-southeast-1b running Relation provider Requirer Interface Type Message postgresql:coordinator postgresql:coordinator coordinator peer postgresql:replication postgresql:replication pgpeer peer
There are several different ways to connect the client and server models together, but for PostgreSQL you should make an offer from the client model, and consume it in the server model. This is because Juju cross model relations are anonymized to avoid namespace clashes and other edge cases; the units in the client model will not know details about the model they are connected to. These details are irrelevant to most charms, but the PostgreSQL charm uses the remote application name to ensure that, when models are redeployed, that the same database credentials are used and the client units are redeployed with the same access to data that they had before. By consuming the offer made by the client model into the server model (and not the other way around), we can control the client application name seen by the PostgreSQL charm and the normal redeployment and disaster recovery processes work as expected.
Once the offer has been consumed, we end up with a proxy of sorts that works like a standard Juju Application; connecting the client Application to the server is done using the normal add-relation command:
$ juju add-relation postgresql:db client-db:db
$ juju wait
$ juju status
Model Controller Cloud/Region Version SLA
server singapore aws/ap-southeast-1 2.3.5 unsupported
SAAS Status Store URL
client-db blocked sydney admin/client.client-db
App Version Status Scale Charm Store Rev OS Notes
postgresql 9.5.12 active 2 postgresql jujucharms 174 ubuntu
Unit Workload Agent Machine Public address Ports Message
postgresql/0* active idle 0 13.229.205.17 5432/tcp Live master (9.5.12)
postgresql/1 active idle 1 13.250.20.84 5432/tcp Live secondary (9.5.12)
Machine State DNS Inst id Series AZ Message
0 started 13.229.205.17 i-0a0ce0ea34e4451da xenial ap-southeast-1a running
1 started 13.250.20.84 i-0c07e2cb0dfd95b69 xenial ap-southeast-1b running
Relation provider Requirer Interface Type Message
postgresql:coordinator postgresql:coordinator coordinator peer
postgresql:db client-db:db pgsql regular
postgresql:replication postgresql:replication pgpeer peer
$ juju switch sydney:admin/client
singapore:admin/server -> sydney:admin/client
$ juju ssh postgresql-client/0
Welcome to Ubuntu 16.04.4 LTS (GNU/Linux 4.4.0-1054-aws x86_64)
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PostgreSQL Client Charm
=======================
To connect to PostgreSQL:
psql service=db_master
psql service=db_1
psql service=db:0_master
psql service=db:0_1
To run a command as administrator (user "root"), use "sudo ".
See "man sudo_root" for details.
ubuntu@ip-172-31-7-119:~$ psql service=db_master
psql (9.5.12)
SSL connection (protocol: TLSv1.2, cipher: ECDHE-RSA-AES256-GCM-SHA384, bits: 256, compression: off)
Type "help" for help.
cli=> create table itsalive(x int);
CREATE TABLE
cli=> \q
ubuntu@ip-172-31-7-119:~$ exit
logout
Connection to 13.210.156.16 closed.
