Template literals

Pandiyan Murugan1 Comment

Template literals in ES6 allows us to embed expressions to our string literals. We can use multi-line strings and string interpolation features with them.

Template literals are enclosed by the back-tick (` `) instead of double or single quotes.

var message = `single line string`;
console.log(message);

// single line string

We can include place holders for string substitution using ${ } syntax

var expression = "place holder"; // string substitution
console.log(`this is a text with ${expression} in a line`);

// this is a text with place holder in a line

We can directly use expression interpolation to embed inline math

var a = 5;
var b = 5;
console.log(`the addition of a+b = ${a+b}`);
// the addition of a+b = 10

We can also call functions and use member functions in strings

function sample() { return "text from sample method"; }
console.log(`yes! ${sample()} and i am in uppercase`.toUpperCase());
// YES! TEXT FROM SAMPLE METHOD AND I AM IN UPPERCASE

The above code retrieves data from sample() method and converts it to uppercase in run-time.

Multiline Strings

We can achieve multi line strings, previously we used to insert new line character in our string

console.log(`First line
Second line`);
// First line 
// Second line

Raw strings

The special raw property, available on the first function argument of tagged template literals, allows you to access the raw strings as they were entered.

String.raw`Hi \n ${2+3}!`;
// "Hi \n 5!"

Tagged template literals

A more advanced form of template literals are tagged template literals. With them we able to modify the output of template literals using a function. The first argument contains an array of string literals. The second, and each argument after the first one, are the values of the processed substitution expressions. We can use any name to our function.

var a = 1;
var b = 2;

function tag(strings, ...values) {
 console.log(strings[0]); // "One "
 console.log(strings[1]); // " Two"
 console.log(strings[2]); // " Three"
 console.log(values[0]); // 1
 console.log(values[1]); // 2
}

tag`One ${ a } Two ${ b } Three`;

// One 
// Two 
// Three
// 1
// 2

Happy exploring ES6 🙂

Elasticsearch Cluster settings for Production Deployment

Pandiyan MuruganLeave a comment

The following settings are needed to set in the configuration in the cluster to achieve high availability and stability.

Data and logs path

By default, the plugins, logs, and data are placed in the installation path. This can lead to unfortunate accidents, whereby the installation directory is accidentally overwritten by a new installation of Elasticsearch. The best thing to do is relocate the data, log, plugins directory outside the installation location as follows

# Path to store data
path.data: /path/to/data1,/path/to/data2

# Path to store log files
path.logs: /path/to/logs

# Path to where plugins are installed
path.plugins: /path/to/plugins

Minimum master nodes

Minimum master node settings prevent split brain, which appears due to the presence of two master in a single cluster. If we have two masters, data integrity becomes perilous, since we have two nodes that think they are in charge. If the split brain happens, there is a possibility of losing data.
This setting should always be configured to a quorum (majority) of your master-eligible nodes. A quorum is (number of master-eligible nodes / 2) +1. In our case currently, we are having 3 nodes so we can set a minimum master node as 2. This setting can be configured as follows in config file

discovery.zen.minimum_master_nodes: 2

The cluster settings can be configured using dynamic API calls also as follows

PUT /_cluster/settings
{
 "persistent" : {
 "discovery.zen.minimum_master_nodes" : 2
 }
}

This setting will become a persistent setting that takes precedence over whatever is in the static configuration.

Default Ping timeout

The node detection process is processed by the discover.zen.fd.ping_timeout property. The ping between nodes will be timed out within 3 seconds in Elasticsearch v1.5.2. This setting can be adjusted if we are facing slowness in the network.

discover.zen.fd.ping_timeout: 30s

Delete all indices settings

The delete index operation can be applied to more than one index or all indices in the cluster using wildcards. In order to avoid this case, we can
disable deleting indices using wild cards by setting action.destructive_requires_name property into true.

PUT /_cluster/settings
{
 "persistent": {
 "action.destructive_requires_name": true
 }
}

Using Unicast over Multicast

Multicast is excellent in the development phase, which will automatically join nodes in the network and forms cluster. But Elasticsearch recommends using Unicast over Multicast in Production. We should provide a list of nodes that need to be present in the cluster. The Unicast can be achieved by setting as follows in the Configuration file

discovery.zen.ping.multicast.enabled: false
discovery.zen.ping.unicast.hosts: ["HOST1", "HOST2", "HOST3"]

Recovery settings

To avoid the shard shuffle on the recovery when the cluster restarts, we need to customized the recovery settings. When cluster restarts, ElasticSearch does not know how many nodes will finally be in the cluster, it tries to balance all known primary shards and replicas to the known machines. When another node suddenly joins the cluster, this whole strategy will change. To avoid the traffic and the overhead of this, ElasticSearch can be configured with a minimum number of nodes it should expect before starting the recovery phase.
The following settings will prevent Elasticsearch from starting until the at least specified number of nodes are present.

gateway.recover_after_nodes: 2

The following settings configures Elasticsearch, how many nodes should be in the cluster, and how long the cluster want to wait for all those
nodes

gateway.expected_nodes: 2
gateway.recover_after_time: 5m

Memory Settings

The ES_HEAP_SIZE environment variable allows setting the heap memory that will be allocated to elasticsearch java process. I already made a detailed post about settings Heap Size in Windows.
The environment variable set with values as follows

ES_HEAP_SIZE
4g

mlockall

To lock the process address space into RAM, preventing any Elasticsearch memory from being swapped out by configuring as follows

bootstrap.mlockall: true

We can check whether settings are applied to the nodes or not by using any one of the following commands

curl http://localhost:9200/_nodes/process?pretty
GET /_nodes/process?pretty

Note that the environment configuration options available during the installation are copied and will be used during the service lifecycle.
This means any changes made to them after the installation will not be picked up unless the service is reinstalled.